Metal oxide-organic hybrid materials for heterogeneous catalysis and methods of making and using thereof

ABSTRACT

Catalysts prepared from abundant, cost effective metals, such as cobalt, nickel, chromium, manganese, iron, and copper, and containing one or more neutrally charged ligands (e.g., monodentate, bidentate, and/or polydentate ligands) and methods of making and using thereof are described herein. Exemplary ligands include, but are not limited to, phosphine ligands, nitrogen-based ligands, sulfur-based ligands, and/or arsenic-based ligands. In some embodiments, the catalyst is a cobalt-based catalyst or a nickel-based catalyst. The catalysts described herein are stable and active at neutral pH and in a wide range of buffers that are both weak and strong proton acceptors. While its activity is slightly lower than state of the art cobalt-based water oxidation catalysts under some conditions, it is capable of sustaining electrolysis at high applied potentials without a significant degradation in catalytic current. This enhanced robustness gives it an advantage in industrial and large-scale water electrolysis schemes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. Ser. No.61/842,621 filed Jul. 3, 2013 and which is incorporated by reference inits entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under Agreement Nos.1122492 and 1119826 awarded by the National Science Foundation, andsupport under Agreement No. DE-FG02-84ER13297 awarded by the Departmentof Energy. The Government has certain rights in the invention.

FIELD OF THE INVENTION

This invention is in the field of catalysis, particularly forapplications in water-oxidation, oxidation of organic species, oxygenreduction, and/or reducing metal ions and/or other species, such asorganic species.

BACKGROUND OF THE INVENTION

The electrochemical production of oxygen from water has been studiedextensively as a component of water-splitting schemes which can be usedin the sustainable generation of hydrogen by electrolysis of water and arenewable energy source, such as sunlight. The water oxidationhalf-reaction may also serve as the anodic half reaction coupled withother aqueous electrochemical reductions, such as electrodeposition ofmetals and/or organic electroreductions. In these schemes, higherefficiency of water oxidation afforded by a catalyst reduces the overallamount of energy needed for these processes. Although some oxides andorganometallic compounds of 2nd and 3rd row transition metals, such asRu, Rh, Ir, and Pt are among the most active water oxidation catalystsknown, their low abundance and the high cost of such metals aresubstantial obstacles to their widespread application.

Cobalt oxides and the recently developed cobaltphosphate/phosphonate/borate compounds (e.g., Co-Pi) offer significantlymore affordable and scalable alternatives. These cobalt catalysts arenot without their drawbacks, however. Their primary method of synthesisis through electrodeposition. These catalysts are prone to degradationat the high currents required for commercial water electrolysis, as wellas in buffers that do not contain a significant concentration ofphosphate, or other strong proton acceptor.

There exists a need for catalysts that do not suffer from thelimitations described above.

Therefore, it is an object of the invention to provide catalysts,particularly oxidation catalysts, that do not suffer from thelimitations described above and methods of making and using thereof.

SUMMARY OF THE INVENTION

Catalysts prepared from d-block transition metals and containing one ormore charged and/or uncharged ligands (e.g., monodentate, bidentate,and/or polydentate ligands) and methods of making and using thereof aredescribed herein. In some embodiments, the d-block transition metal isone that forms stable carbonyl complexes. Exemplary metals include, butare not limited to, cobalt (Co), nickel (Ni), chromium (Cr), manganese(Mn), iron (Fe), copper (Cu), Rhodium (Rh), and/or Iridium (Ir).Exemplary ligands include, but are not limited to, phosphine ligands,nitrogen-based ligands (e.g., diamines, N-containing heterocycles),sulfur-based ligands, and/or arsenic-based ligands. In some embodiments,the catalyst is a cobalt-based catalyst, nickel-based catalyst,rhodium-based catalyst, or iridium-based catalyst.

The catalysts described herein are stable to a maximum overpotential ofat least about 500, 550, 600, 650, 700, 750, 780, or 800 Mv at neutralpH or at least about 500, 550, 600, 650, 700, 750, 780, 800, 900, 1000,1100, or 1200 mV at alkaline pH. For example, the catalysts describedherein were subjected to a potential 300 mV higher than the limitreported for Nocera's catalyst. No change in the catalyst/catalyticactivity over 40 hours; little or no Co and/or P was found in theelectrolyte solution when assayed using ICP-MS. The catalysts can beused in any of the commonly used electrolyte systems, such as borate,phosphate buffers, hydroxide, nitrate, and/or sulfate.

The catalysts described herein are stable and active at neutral pH, in awide range of buffers that are both weak and strong proton acceptors,and at highly basic pH, e.g., greater than 10, such as pH 13 to 30 wt %KOH, and in the presence of high concentrations of soluble metal ions,such as Zn²⁺. The examples show that catalysts are stable at stronglyalkaline pH for a period of at least 20, 30, 40, 50, 60, 70, 80, 90, 100days or greater.

While the activity of the cobalt-based catalyst described herein isslightly lower than state of the art cobalt-based water oxidationcatalysts under some conditions, the cobalt-based catalyst is capable ofsustaining electrolysis at high applied potentials without a significantdegradation in catalytic current. This enhanced robustness gives it anadvantage in industrial and large-scale water electrolysis schemes.

The catalysts described herein can be incorporated into theoxygen-producing anode of a variety of devices for purposes including,but not limited to, splitting water by electrolysis to produce hydrogenat the cathode, splitting water by electrolysis to produce oxygen at theanode, reducing metal ions to their corresponding metallic neutral stateat the cathode, reduction of organic species by electrolysis at thecathode, reduction of any other species at the cathode, as long as it iscoupled with oxygen production at the anode, and combinations thereof.These electrolytic processes can be driven by a variety of energysources, such as solar, wind, and/or nuclear.

Being potent enough to oxidize water, these catalysts are also capableof oxidizing a wide range of organic compounds with applications towardoxidative synthesis of specialized chemicals, as well as degradation ofharmful organic species.

The catalysts described herein can also be incorporated into theoxygen-consuming cathode of a variety of devices including, but notlimited to, oxygen-scavenging devices, oxygen-detectors, and fuel cellsor batteries which consume oxygen (pure, or in mixtures, such as air, orspecialty gas mixtures) in addition to any fuel including, but notlimited to, hydrogen, organic fuels, metallic fuels, or inorganic fuels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of the apparatus used for destructivedistillation.

FIG. 2 is a graph showing cyclic voltammograms of cobalt catalysts withdifferent organophosphines incorporated: dppe; Xantphos;triphenylphosphine; and DPEphos.

FIG. 3 is a graph showing 10 minute chronoamperograms of samples at 1.2V vs. Ag/AgCl taken prior to Tafel plots at pH 7 in 0.1 M nitrate,sulfate, acetate, phosphate, and borate buffers. Control samples weretaken in different buffers using an FTO/glass slide without any catalyst(grey).

FIG. 4 is a graph showing the Tafel plot of Co-dppe in pH 13 NaOH.

FIG. 5 is a graph showing hour-long chronoamperograms of Co-dppe inphosphate buffer at pH 7 at 1.1 V vs. Ag/AgCl (bottom), 1.2 V vs.Ag/AgCl (middle), and 1.3 V vs. Ag/AgCl (top).

FIGS. 6A and 6B are graphs showing current stability data for a Co-dppesample with geometric surface area 1.45 cm² showing both continuous 12 hstability at 1.6 V vs. NHE (left) and stable activity over a one hourtime course after >40 h intermittent use (right). Brief drops and spikesobserved in the current in the inset figure are caused by oxygen bubbleformation and release.

FIG. 7 is a graph showing a 1 hour chronoamperogram in a pH 7 sulfatebuffered solution at potentials of 1.1, 1.2, 1.3, and 1.4 V vs. Ag/AgCland a 1 hour chronoamperogram in the same sulfate solution (at 1.3 V vs.Ag/AgCl) using a sample previously used for 12 h of water oxidation inborate at 1.4 V vs. Ag/AgCl. Activity in a weakly basic electrolyte isstill present.

FIG. 8 is a graph showing continuous current stability for 50 h with aCo-dppe sample with geometric area 1.45 cm² in water collected from theLong Island Sound that has been passed through a 0.2 micron filter, butotherwise unadulterated.

FIG. 9 is a graph showing current density (A/cm²) as a function ofapplied voltage (V vs Ni metal in same electrolyte) for catalyst-coatedand uncoated nickel electrodes in 25 wt % potassium hydroxide.

FIGS. 10A-M are cyclic voltammograms (3 cycles each) in pH 7.0 borate ofcobalt-based catalysts with different ligands. The ligands are shownstructurally in each voltammogram Materials formed from CO₂(CO)₈ anddppe, (FIG. 10A), 1,2-ethanediylbis[diphenylphosphine oxide] (FIG. 10B),DPEphos (FIG. 10C), triphenylphosphine (FIG. 10D), 2,2′-bipyridine (FIG.10E), TMEDA or EDTA (FIG. 10F); materials formed from1,2-Bis(1-piperidinyl)ethane (FIG. 10G), dppm (FIG. 10H), dppb (FIG.10I), dppp (FIG. 10J) andN¹,N^(1′),N²,N^(2′)-tetramethylethane-1,2-diamine (FIG. 10K);4,4′-bipyridine (FIG. 10L); FIG. 10M is a control without catalyst.

FIG. 11A is a graph showing current density (A/cm²) as a function ofapplied potential (V vs Ni) with catalyst and no catalyst in 25 wt %sodium hydroxide and 30 g/L zinc oxide. FIG. 11B is a graph showingcurrent density (A/cm²) as a function of applied potential (V vs Ni)with catalyst and no catalyst in 25 wt % sodium hydroxide saturated withzinc oxide.

FIGS. 12 A-F are graphs showing cell current (A) as a function of cellpotential (V) with and without catalyst at day 1, 13, 20, 34, 42, and50.

FIG. 13 is a graph showing the relative absorption for various timestreated with catalyst as a function of time (minutes).

FIG. 14 is a graph showing the absorbance for Orange G dye as a functionof catalyst concentration (nM) over time (minutes).

FIG. 15 is a graph showing the effect of catalyst loading on the rate ofdye bleaching.

FIG. 16 is an illustration of a dry-cell alkaline electrolyzer used inExample 5 (solid lines represent electrodes and dashed lines presentcatalyst coating).

DETAILED DESCRIPTION OF THE INVENTION I. Definitions

“Water oxidation catalyst”, “WOC”, “oxygen evolving catalyst”, and “OEC”are used interchangeably and refer to a catalyst used to oxidize waterto form oxygen (O₂) and hydrogen (H⁺) ions. Oxygen yield can bemonitored using a variety of techniques. In one embodiment, oxygen yieldis monitored using phase-shift fluorescence detection.

“Heterogeneous”, as used herein, refers to the form of catalysis wherethe phase of the catalyst differs from that of the reactants

“Homogeneous”, as used herein, means the catalyst is soluble (i.e., samephase as the reactants) in the reaction solution.

“Oxidatively stable” as used herein, means that more than 90%, more than92%, more than 94%, more than 95%, more than 98%, more than 99%, morethan 99.5%, more than 99.9%, more than 99.95%, more than 99.99% of thecatalyst is structurally intact in the presence of one or more oxidantsincluding, but not limited to, O₂, O₃, and peroxides, at a high appliedpotential (0.5-3.0 V vs Ag/AgCl) over a broad pH range (e.g., 6-16) forat least 7 days, 14 days, 21, days, 28 days, 30 days, 45 days, twomonths, three months, four months, five months, six months, one year, orlonger at ambient temperature and ambient light conditions.Alternatively, the catalyst undergoes less than 10%, less than 5%, lessthan 1%, less than 0.5%, less than 0.1%, less than 0.05%, or less than0.01% oxidation under the conditions described above

“Hydrolytically stable”, as used herein, means that more than 90%, morethan 92%, more than 94%, more than 95%, more than 98%, more than 99%,more than 99.5%, more than 99.9%, more than 99.95%, more than 99.99% ofthe catalyst is structurally intact in the presence of water over abroad pH range (e.g., 6-16) for at least 7 days, 14 days, 21, days, 28days, 30 days, 45 days, two months, three months, four months, fivemonths, six months, one year, or longer at ambient temperature andambient light conditions. Alternatively, the catalyst undergoes lessthan 10%, less than 5%, less than 1%, less than 0.5%, less than 0.1%,less than 0.05%, or less than 0.01% hydrolysis under the conditionsdescribed above. In a particular embodiment, the catalyst undergoes nostructural changes under the conditions described above.

“Thermally stable”, as used herein, means that more than 90%, more than92%, more than 94%, more than 95%, more than 98%, more than 99%, morethan 99.5%, more than 99.9%, more than 99.95%, more than 99.99% of thecatalyst is structurally intact at room temperature or lower or whenheated to a temperature above room temperature. In a particularembodiment, the catalyst undergoes no structural changes when heatedabove room temperature.

“Turn over number” or “TON”, as used herein, means the number of molesof substrate that a mole of catalyst can convert before beinginactivated. TON is calculated as the number of moles of oxygen, n_(O2),divided by the number of moles of catalyst, n_(cat).

“Turn over frequency” or “TOF”, as used herein, refers to the turnoverper unit time under turnover conditions. It is typically expressed ins⁻¹. The TOF can be calculated by dividing the TON by the time period,in seconds, over which the TON was measured.

“Turnover conditions”, as used herein, refers to the conditions in whichthe catalytic reaction takes place. “Turnover conditions” include at aminimum pH and temperature. Other criteria include concentration of theoxidant and concentration of the WOC. The turnover conditions can varyfor a given WOC.

“Oxygen yield”, as used herein, refers to the percent oxygen formedduring the catalytic reaction. It is expressed as a percent by weight ofan oxidant or sacrificial electron acceptor.

“Oxidant” or “sacrificial electron acceptor”, as used herein, refers tothe molecule that is reduced during the oxidation of water.

“Light collecting molecule”, as used herein, refers to the molecule inthe catalytic system that absorbs light creating a charge separatedexcited state.

“Hydrogen reduction catalyst” and “hydrogen evolving catalyst” are usedinterchangeably and refer to a catalyst which reduce protons to formhydrogen gas.

“Alkyl”, as used herein, refers to the radical of saturated orunsaturated aliphatic groups, including straight-chain alkyl,heteroalkyl, alkenyl, or alkynyl groups, branched-chain alkyl, alkenyl,or alkynyl groups, cycloalkyl, cycloalkenyl, or cycloalkynyl (alicyclic)groups, alkyl substituted cycloalkyl, cycloalkenyl, or cycloalkynylgroups, and cycloalkyl substituted alkyl, alkenyl, or alkynyl groups. Insome embodiments, a straight chain or branched chain alkyl has 30 orfewer carbon atoms in its backbone (e.g., C₁-C₃₀ for straight chain,C₃-C₃₀ for branched chain), more preferably 20 or fewer carbon atoms,more preferably 12 or fewer carbon atoms, and most preferably 8 or fewercarbon atoms. Likewise, preferred cycloalkyls have from 3-10 carbonatoms in their ring structure, and more preferably have 5, 6 or 7carbons in the ring structure. The ranges provided above are inclusiveof all values between the minimum value and the maximum value.

The term “alkyl” includes “heteroalkyls”, “unsubstituted alkyls”, and“substituted alkyls”, the latter of which refers to alkyl moietieshaving one or more substituents replacing a hydrogen on one or morecarbons of the hydrocarbon backbone. Such substituents include, but arenot limited to, halogen, hydroxyl, carbonyl (such as a carboxyl,alkoxycarbonyl, formyl, or an acyl), thiocarbonyl (such as a thioester,a thioacetate, or a thioformate), alkoxyl, phosphoryl, phosphate,phosphonate, a phosphinate, amino, amido, amidine, imine, cyano, nitro,azido, sulfhydryl, alkylthio, sulfate, sulfonate, sulfamoyl,sulfonamido, sulfonyl, heterocyclyl, aralkyl, or an aromatic orheteroaromatic moiety.

Unless the number of carbons is otherwise specified, “lower alkyl” asused herein means an alkyl group, as defined above, but having from oneto ten carbons, more preferably from one to six carbon atoms in itsbackbone structure. Likewise, “lower alkenyl” and “lower alkynyl” havesimilar chain lengths. Preferred alkyl groups are lower alkyls.

The alkyl groups may also contain one or more heteroatoms within thecarbon backbone. Preferably the heteroatoms incorporated into the carbonbackbone are oxygen, nitrogen, sulfur, and combinations thereof. Incertain embodiments, the alkyl group contains between one and fourheteroatoms.

“Alkenyl” and “Alkynyl”, as used herein, refer to unsaturated aliphaticgroups containing one or more double or triple bonds analogous in length(e.g., C₂-C₃₀) and possible substitution to the alkyl groups describedabove.

“Aryl”, as used herein, refers to 5-, 6- and 7-membered aromatic ring.The ring may be a carbocyclic, heterocyclic, fused carbocyclic, fusedheterocyclic, bicarbocyclic, or biheterocyclic ring system, optionallysubstituted by halogens, alkyl-, alkenyl-, and alkynyl-groups. Broadlydefined, “Ar”, as used herein, includes 5-, 6- and 7-memberedsingle-ring aromatic groups that may include from zero to fourheteroatoms, for example, benzene, pyrrole, furan, thiophene, imidazole,oxazole, thiazole, triazole, pyrazole, pyridine, pyrazine, pyridazineand pyrimidine, and the like. Those aryl groups having heteroatoms inthe ring structure may also be referred to as “heteroaryl”, “arylheterocycles”, or “heteroaromatics”. The aromatic ring can besubstituted at one or more ring positions with such substituents asdescribed above, for example, halogen, azide, alkyl, aralkyl, alkenyl,alkynyl, cycloalkyl, hydroxyl, alkoxyl, amino, nitro, sulfhydryl, imino,amino, phosphonate, phosphinate, carbonyl, carboxyl, silyl, ether,alkylthio, sulfonyl, sulfonamido, ketone, aldehyde, ester, heterocyclyl,aromatic or heteroaromatic moieties, —CF₃, —CN, or the like. The term“Ar” also includes polycyclic ring systems having two or more cyclicrings in which two or more carbons are common to two adjoining rings(the rings are “fused rings”) wherein at least one of the rings isaromatic, e.g., the other cyclic rings can be cycloalkyls,cycloalkenyls, cycloalkynyls, aryls and/or heterocycles. Examples ofheterocyclic ring include, but are not limited to, benzimidazolyl,benzofuranyl, benzothiofuranyl, benzothiophenyl, benzoxazolyl,benzoxazolinyl, benzthiazolyl, benztriazolyl, benztetrazolyl,benzisoxazolyl, benzisothiazolyl, benzimidazolinyl, carbazolyl, 4aHcarbazolyl, carbolinyl, chromanyl, chromenyl, cinnolinyl,decahydroquinolinyl, 2H,6H-1,5,2-dithiazinyl, dihydrofuro[2,3b]tetrahydrofuran, furanyl, furazanyl, imidazolidinyl, imidazolinyl,imidazolyl, 1H-indazolyl, indolenyl, indolinyl, indolizinyl, indolyl,3H-indolyl, isatinoyl, isobenzofuranyl, isochromanyl, isoindazolyl,isoindolinyl, isoindolyl, isoquinolinyl, isothiazolyl, isoxazolyl,methylenedioxyphenyl, morpholinyl, naphthyridinyl,octahydroisoquinolinyl, oxadiazolyl, 1,2,3-oxadiazolyl,1,2,4-oxadiazolyl, 1,2,5-oxadiazolyl, 1,3,4-oxadiazolyl, oxazolidinyl,oxazolyl, oxindolyl, pyrimidinyl, phenanthridinyl, phenanthrolinyl,phenazinyl, phenothiazinyl, phenoxathinyl, phenoxazinyl, phthalazinyl,piperazinyl, piperidinyl, piperidonyl, 4-piperidonyl, piperonyl,pteridinyl, purinyl, pyranyl, pyrazinyl, pyrazolidinyl, pyrazolinyl,pyrazolyl, pyridazinyl, pyridooxazole, pyridoimidazole, pyridothiazole,pyridinyl, pyridyl, pyrimidinyl, pyrrolidinyl, pyrrolinyl, 2H-pyrrolyl,pyrrolyl, quinazolinyl, quinolinyl, 4H-quinolizinyl, quinoxalinyl,quinuclidinyl, tetrahydrofuranyl, tetrahydroisoquinolinyl,tetrahydroquinolinyl, tetrazolyl, 6H-1,2,5-thiadiazinyl,1,2,3-thiadiazolyl, 1,2,4-thiadiazolyl, 1,2,5-thiadiazolyl,1,3,4-thiadiazolyl, thianthrenyl, thiazolyl, thienyl, thienothiazolyl,thienooxazolyl, thienoimidazolyl, thiophenyl and xanthenyl.

“Alkylaryl”, as used herein, refers to an alkyl group substituted withan aryl group (e.g., an aromatic or hetero aromatic group).

“Heterocycle” or “heterocyclic”, as used herein, refers to a cyclicradical attached via a ring carbon or nitrogen of a monocyclic orbicyclic ring containing 3-10 ring atoms, and preferably from 5-6 ringatoms, consisting of carbon and one to four heteroatoms each selectedfrom the group consisting of non-peroxide oxygen, sulfur, and N(Y)wherein Y is absent or is H, O, (C₁₋₄) alkyl, phenyl or benzyl, andoptionally containing one or more double or triple bonds, and optionallysubstituted with one or more substituents. The term “heterocycle” alsoencompasses substituted and unsubstituted heteroaryl rings. Examples ofheterocyclic ring include, but are not limited to, benzimidazolyl,benzofuranyl, benzothiofuranyl, benzothiophenyl, benzoxazolyl,benzoxazolinyl, benzthiazolyl, benztriazolyl, benztetrazolyl,benzisoxazolyl, benzisothiazolyl, benzimidazolinyl, carbazolyl,4aH-carbazolyl, carbolinyl, chromanyl, chromenyl, cinnolinyl,decahydroquinolinyl, 2H,6H-1,5,2-dithiazinyl,dihydrofuro[2,3-b]tetrahydrofuran, furanyl, furazanyl, imidazolidinyl,imidazolinyl, imidazolyl, 1H-indazolyl, indolenyl, indolinyl,indolizinyl, indolyl, 3H-indolyl, isatinoyl, isobenzofuranyl,isochromanyl, isoindazolyl, isoindolinyl, isoindolyl, isoquinolinyl,isothiazolyl, isoxazolyl, methylenedioxyphenyl, morpholinyl,naphthyridinyl, octahydroisoquinolinyl, oxadiazolyl, 1,2,3-oxadiazolyl,1,2,4-oxadiazolyl, 1,2,5-oxadiazolyl, 1,3,4-oxadiazolyl, oxazolidinyl,oxazolyl, oxindolyl, pyrimidinyl, phenanthridinyl, phenanthrolinyl,phenazinyl, phenothiazinyl, phenoxathinyl, phenoxazinyl, phthalazinyl,piperazinyl, piperidinyl, piperidonyl, 4-piperidonyl, piperonyl,pteridinyl, purinyl, pyranyl, pyrazinyl, pyrazolidinyl, pyrazolinyl,pyrazolyl, pyridazinyl, pyridooxazole, pyridoimidazole, pyridothiazole,pyridinyl, pyridyl, pyrimidinyl, pyrrolidinyl, pyrrolinyl, 2H-pyrrolyl,pyrrolyl, quinazolinyl, quinolinyl, 4H-quinolizinyl, quinoxalinyl,quinuclidinyl, tetrahydrofuranyl, tetrahydroisoquinolinyl,tetrahydroquinolinyl, tetrazolyl, 6H-1,2,5-thiadiazinyl,1,2,3-thiadiazolyl, 1,2,4-thiadiazolyl, 1,2,5-thiadiazolyl,1,3,4-thiadiazolyl, thianthrenyl, thiazolyl, thienyl, thienothiazolyl,thienooxazolyl, thienoimidazolyl, thiophenyl and xanthenyl.

“Heteroaryl”, as used herein, refers to a monocyclic aromatic ringcontaining five or six ring atoms consisting of carbon and 1, 2, 3, or 4heteroatoms each selected from the group consisting of non-peroxideoxygen, sulfur, and N(Y) where Y is absent or is H, O, (C₁-C₈) alkyl,phenyl or benzyl. Non-limiting examples of heteroaryl groups includefuryl, imidazolyl, triazolyl, triazinyl, oxazoyl, isoxazoyl, thiazolyl,isothiazoyl, pyrazolyl, pyrrolyl, pyrazinyl, tetrazolyl, pyridyl, (orits N-oxide), thienyl, pyrimidinyl (or its N-oxide), indolyl,isoquinolyl (or its N-oxide), quinolyl (or its N-oxide) and the like.The term “heteroaryl” can include radicals of an ortho-fused bicyclicheterocycle of about eight to ten ring atoms derived therefrom,particularly a benz-derivative or one derived by fusing a propylene,trimethylene, or tetramethylene diradical thereto. Examples ofheteroaryl can be furyl, imidazolyl, triazolyl, triazinyl, oxazoyl,isoxazoyl, thiazolyl, isothiazoyl, pyraxolyl, pyrrolyl, pyrazinyl,tetrazolyl, pyridyl (or its N-oxide), thientyl, pyrimidinyl (or itsN-oxide), indolyl, isoquinolyl (or its N-oxide), quinolyl (or itsN-oxide), and the like.

“Halogen”, as used herein, refers to fluorine, chlorine, bromine, oriodine.

The term “substituted” as used herein, refers to all permissiblesubstituents of the compounds described herein. In the broadest sense,the permissible substituents include acyclic and cyclic, branched andunbranched, carbocyclic and heterocyclic, aromatic and nonaromaticsubstituents of organic compounds. Illustrative substituents include,but are not limited to, halogens, hydroxyl groups, or any other organicgroupings containing any number of carbon atoms, preferably 1-14 carbonatoms, and optionally include one or more heteroatoms such as oxygen,sulfur, or nitrogen grouping in linear, branched, or cyclic structuralformats. Representative substituents include alkyl, substituted alkyl,alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, phenyl,substituted phenyl, aryl, substituted aryl, heteroaryl, substitutedheteroaryl, halo, hydroxyl, alkoxy, substituted alkoxy, phenoxy,substituted phenoxy, aroxy, substituted aroxy, alkylthio, substitutedalkylthio, phenylthio, substituted phenylthio, arylthio, substitutedarylthio, cyano, isocyano, substituted isocyano, carbonyl, substitutedcarbonyl, carboxyl, substituted carboxyl, amino, substituted amino,amido, substituted amido, sulfonyl, substituted sulfonyl, sulfonic acid,phosphoryl, substituted phosphoryl, phosphonyl, substituted phosphonyl,polyaryl, substituted polyaryl, C₃-C₂₀ cyclic, substituted C₃-C₂₀cyclic, heterocyclic, substituted heterocyclic, aminoacid, peptide, andpolypeptide groups.

Heteroatoms such as nitrogen may have hydrogen substituents and/or anypermissible substituents of organic compounds described herein whichsatisfy the valences of the heteroatoms. It is understood that“substitution” or “substituted” includes the implicit proviso that suchsubstitution is in accordance with permitted valence of the substitutedatom and the substituent, and that the substitution results in a stablecompound, i.e. a compound that does not spontaneously undergotransformation such as by rearrangement, cyclization, elimination, etc.

II. Catalysts

Catalysts that exhibit several differences from previously identifiedoxide materials are described herein. The catalysts show improvedstability at high overvoltages (600-800 mV), with weakly basicelectrolytes (SO₄ ²⁻ and NO₃ ⁻), and overvoltages up to or greater than1200 mV in strongly basic conditions, e.g., greater than pH 10, such aspH 12 to 30 wt % KOH.

In some embodiments, the catalyst has the formula:MY_(a)(CO)_(b)O_(c)(OH)_(d)(H₂O)_(e)wherein

M is a d-block transition metal, preferably one that forms stablecarbonyl complexes;

Y is a mondentate ligand, bidentate ligand, polydentate ligand, orcombination thereof;

a is any value from 0-3, preferably 0.5-1;

b is any value from 0-3, preferably 0-2;

c is any value from 1-4, preferably 1.5-3;

d is any value from 0-4; and

e is any value from 0-6.

In some embodiments, M includes, but is not limited to, Cr, Mn, Fe, Co,Ni, Cu, Rh, Ir, or combinations thereof.

In some embodiments, M is Co and/or Ni.

In some embodiments, M is Co and/or Ni and the preferred values for a-eare as described above.

In some embodiments, the ligands are not charged, i.e., have no chargedatoms. The use of neutral ligands to prepare metal oxide-basedheterogeneous catalysts is generally not found in the art. In someembodiments, the ligands are charged, wherein the charge resides on anatom or atoms that does participate in a bond or coordination with themetal. In contrast, the ligands in most prior art catalyst systems, suchas Nocera's catalyst, are charged at the site of interaction with themetal, likely to enhance solubility to facilitate synthesis.

In some embodiments, M and a-e are as defined above, and Y is aphosphorus-based ligand. In particular embodiments, the phosphorus-basedligand is selected from P-heterocycles, or primary, secondary ortertiary phosphines with alkyl, aryl or heteroatom substituents,primary, secondary, or tertiary phosphine oxides with alkyl, aryl, orheteroatom substituents, or any combination thereof. In more particularembodiments, the ligand is an alkyl diaryl phosphine or a triaylphosphine. Exemplary alkyldiaryl phosphines include, but are not limitedto, dppe. Exemplary triaryl phosphines include, but are not limited toXantphos, triphenylphosphine, DPEphos,1,2-ethanediylbis[diphenylphosphine oxide],1,1-Bis(diphenylphosphino)methane (dppm),1,1-Bis(diphenylphosphino)ethane (dppe),1,1-Bis(diphenylphosphino)propane (dppp),1,1-Bis(diphenylphosphino)butane (dppb), and combinations thereof.

The selection of phosphine ligands is counterintuitive as such ligandsare notoriously susceptible to oxidation (to P═O) or other types ofdegradation under the conditions used to prepare the catalysts describedherein. However, no such oxidation or degradation was observed during orafter synthesis. In some embodiments, during working conditions, partialdegradation of the ligand is observed. In other embodiments, duringworking conditions, complete degradation of the ligand is observed;however the structural integrity and activity of the nanoparticle isretained.

ICP-MS data show that for cobalt-phosphine-based catalysts, the P:Coatomic ratio is typically between 1:1 and 1:2. The phosphine ligand mayhelp stabilize the particles and inhibit Co leaching typically seen inprior art cobalt-based catalysts. By incorporating an organic phosphineunit, the solubility of the material in water is minimized, increasingthe stability of the material under aqueous conditions. This propertymay result from the water-insolubility of the phosphine unit. Thisincreased stability allows for use of cheaper electrolytes and highercurrents.

In other embodiments, M and a-e are as defined above and the bidentateligand is a nitrogen-based ligand, a sulfur-based ligand, anarsenic-based ligand, any combination thereof, or any combination with aphosphine. In particular embodiments, the nitrogen-based ligand isselected from N-heterocycles, or primary, secondary or tertiary amines,with alkyl and/or aryl substituents; the sulfur-based ligand is selectedfrom S-heterocycles, or alkyl and/or aryl thioethers; the arsenic-basedligand is selected from As-heterocycles or any tertiary arsine withalkyl and/or aryl substituents. Exemplary nitrogen-based ligandsinclude, but are not limited to, 1,2-Bis(1-piperidinyl)ethane, TMEDA,EDTA, 2, T-bipyridine, and combinations thereof.

The ligands can contain one or more alkyl and/or aryl groups as definedabove. The alkyl and/or aryl groups can be substituted or unsubstituted.Suitable substituents are known in the art and include, but are notlimited to, halogens, hydroxyl groups, nitro, alkyl, substituted alkyl,alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, phenyl,substituted phenyl, aryl, substituted aryl, heteroaryl, substitutedheteroaryl, alkoxy, substituted alkoxy, phenoxy, substituted phenoxy,aroxy, substituted aroxy, alkylthio, substituted alkylthio, phenylthio,substituted phenylthio, arylthio, substituted arylthio, cyano, isocyano,substituted isocyano, carbonyl, substituted carbonyl, carboxyl,substituted carboxyl, amino, substituted amino, amido, substitutedamido, sulfonyl, substituted sulfonyl, sulfonic acid, phosphoryl,substituted phosphoryl, phosphonyl, substituted phosphonyl, polyaryl,substituted polyaryl, C₃-C₂₀ cyclic, substituted C₃-C₂₀ cyclic,heterocyclic, and substituted heterocyclic groups.

A. Heterogeneous Catalysts

The catalysts described herein can be used as heterogeneous catalysts.The catalysts can be readily applied as coating or layer to a substrate,such as the surface of an electrode. The coating or layer can be castfrom suspension, and do not require an external stimulus (e.g., current(electrochemical) or heat) for layer formation. In some embodiments, thesurface is densely or sparsely studded with particles of catalyst. Thenecessary loading is low enough that a fully coated electrode is stillcompletely transparent, which is beneficial for use in photovoltaic orphotochemical cells.

The catalysts described herein can be coated on a variety of substratesincluding, but not limited to, conductive substrates, photocatalyticsubstrates, and combinations thereof. Exemplary substrates include, butare not limited to, oxides, such as tin-doped indium oxide (ITO),fluorine doped tin oxide (FTO), tin oxide (SnO₂), tungsten oxide (WO₃),iron oxide (Fe₂O₃), and titanium dioxide (TiO₂); carbon-based electrodes(typically used in fuel cells), such as glassy carbon, wooly carbon, andconductive carbon fiber; and metals, such as aluminum, copper, iron,lead, nickel, silver, stainless steel, titanium, and zinc, or any alloyscontaining these metals. Many of these metals oxidize easily, so it ispossible the catalyst adheres to an oxide layer on the metal surface andnot the metal itself.

The catalysts described herein are likely nanomaterials (e.g.,nanoparticles) rather than molecular catalysts. The average diameter ofthe particles can vary. However, in some embodiments, the averagediameter is from about 1 to 500 nm, preferably from about 5 to about 400nm, more preferably from about 5 to about 300 nm, more preferably fromabout 10 nm to about 300 nm, most preferably from about 15 nm to about300 nm. In some embodiments, the catalyst is largely amorphous asmeasured by HRTEM and XRD.

In some embodiments, the nanomaterial contains a core unit containing aplurality of metal (e.g., cobalt) atoms. In some embodiments, the numberof metal atoms is from about 2 to about 20, preferably from about 4 toabout 16. The metal atoms are surrounded by oxygen atoms, possibly in acubane structure. The cubane structure can be decorated and/orinterconnected by the phosphine ligands and/or other types of ligands.

In some embodiments, upon coating onto a substrate, a substantial amountof the catalyst detaches from the surface leaving roughly 15-20% of thesubstrate surface coated with the catalyst. However, even at theserelatively sparsely-coated areas, the catalysts described herein exhibitsignificantly higher activity per mass of cobalt than Nocera's family ofCo-Xi catalysts (where Xi is an inorganic oxyanion; X=P, MeP, B, etc.),which are deposited as a film electrochemically and necessarilythoroughly coat the electrode surface. The fact that less materials canbe used to achieved the same or better performance than the prior artcatalysts should result in lower cost which is important for largerscale commercial applications.

The catalysts described herein are stable over a broad pH range, such asabout 4.0 to over 14 or 30 wt % KOH, preferably from about 6.0 to about10, more preferably from about 4.5 to about 9.5. The catalysts describedherein are also active for prolonged periods in unadulterated sea wateror preferably sea water containing additives, such as borate orhydroxide. The additives increase the ionic strength (decrease electricresistance of the electrolyte) and/or improve the proton-acceptingcapability of the electrolyte. Some prior art catalysts, such asNocera's, require addition of phosphate or borate to naturally sourcedwaters, to avoid catalyst deactivation. Other prior art catalystsrequire the addition of strong acids or bases to perform wateroxidation.

The catalysts described herein are stable to a maximum overpotential ofat least about 500, 550, 600, 650, 700, 750, 780, 800, 900, 1000, 1100,1200 Mv or greater. For example, the catalysts described herein weresubjected to a potential 300 mV higher than the limit reported forNocera's catalyst (both at pH 7). No change in the catalyst/catalyticactivity over 12 hours; little or no Co and/or P was found in theelectrolyte solution when assayed using ICP-MS. The catalysts can beused in any of the commonly used buffer systems, such as borate,phosphate, nitrate, and/or sulfate.

The catalysts described herein can be prepared by a simple, scalablemethod that does not require electrochemical deposition or annealing.

Table 1 summarizes the performance differences between some of thecatalysts described herein and catalysts known in the art.

TABLE 1 Summary of performance characteristics of various catalystsCatalyst Co-based Best Co oxide catalysts type described Nocera Fe—Co—Niherein (borate, (phosphate, Oxide pH 7) pH 7) (Berlingette) Minimum 400mV 380 mV 250 mV Objective (linear at (linear at (linear at 190 mV)Overpotential 275 mV) 275 mV) (at 0.5 mA/cm²) Maximum 780 mV 480 mV highSustainable Overpotential pH range 6-16 4.5-9.5 >13 Electrolyte Best inborate Only stable in Requires very Limitations and hydroxide. strongproton high pH Stable in all acceptors (KOH) and tested (acetate,(phosphate, non- phosphate, borate) coordinating nitrate, sulfate,electrolyte borate, hydroxide, zincate) Other Must be Difficult andDrawbacks prepared on expensive to conductive prepare substrate

The catalysts described herein are stable at much higher overpotentialsthan Nocera's catalyst and are stable over a much broader pH range thanthe known best-forming Co-oxide catalysts. While the catalysts describedherein and Nocera's catalysts are active at neutral pHs, Nocera'scatalyst requires buffers having high proton accepting capacity. Thecatalysts described herein have little or no electrolyte limitations,which is in sharp contrast to Nocera's catalyst and Co-oxide catalysts.

III. Methods of Making the Catalysts

The catalysts can be prepared using various methods known in the art.The synthesis is a simple, scalable chemical reaction that does notrequire electrochemical deposition, ultra-high vacuum conditions, orannealing, which are drawbacks in many state of the art preparations.The synthesis is easily adaptable for use with other metals or ligands.It has been shown that small differences in ligand structure affect theactivity profile of the catalyst. Therefore, one can have a high degreeof control of catalyst properties based on selection of ligand.

A. Cobalt-Based Catalysts

In one embodiment, the cobalt-based catalysts are prepared bythermolysis of a solution of a suitable cobalt precursor, such asdicobalt octacarbonyl, and a suitable phosphine ligand, such as abidentate phosphine (e.g., 1,2-bis(diphenylphosphino)ethane (dppe,))under an inert atmosphere.

The thermolysis reaction resulted in a decrease in mass by 20-28% (5-7equiv. CO lost from Co₂(CO)₈). Subsequent aerobic oxidation of theresulting black precipitate at ambient temperature increased the mass by5-12%, and afforded the resulting Co-dppe catalyst a light brown,nanoparticulate precipitate.

TEM studies revealed roughly spherical particles with large sizedispersity (15-300 nm in diameter) and a high degree of aggregation. EDXmeasurements from several particles of assorted sizes indicated anapproximate Co:P ratio between 1:1 and 2:1.

Combined ICP-MS and C, H, N combustion analyses showed 1 to have a bulkcomposition of 16.8% Co, 8.7% P, 45.3% C and 4.0% H by mass, indicatinga stoichiometry of 2 Co atoms per molecule of dppe. No significantamount (<0.5 ppm) of Ir, Ru, Rh or Pt was found, excluding thepossibility that the activity is due to impurities of these metals.

The FT-IR spectrum is distinct from those reported for CoO and Co₃O₄.Closer analysis indicates presence of metal-bound CO as well as cobaltoxide clusters. The small number of sharp Co-0 vibrational bands(500-800 cm⁻¹) suggests fairly small clusters of high symmetry, whichare more likely modified oxocubane than adamantane structures.

Despite the insolubility of the resulting Co-dppe catalyst in everysolvent tested, solid-state 31P NMR identified one broad signal (δ≈32ppm, 1.5 kHz width at half maximum). These values are consistent withthose of known complexes of dppe and ⁵⁹Co. Additionally, unmodified dppewas recovered by destructive distillation of the Co-dppe catalyst,indicating that the phosphine was not oxidized or otherwise covalentlymodified during the synthesis of the Co-dppe catalyst.

Glass slides with a 500 inn film of fluorine-doped tin oxide (FTO) onone side were used as electrodes. Application of a suspension of theCo-dppe catalyst in ethyl acetate to the FTO face of an electrode,followed by air-drying, afforded the active electrodes.Post-electrolysis SEM studies indicated that the catalyst particlesbecome tightly bound to the surface with controllable filling fraction.“Tightly bound”, as used herein, generally means that the catalystremains adhered to the substrate under varying conditions, such as pH,solvent, etc. while retaining catalytic activity.

Cyclic voltammograms of an electrode with 1 mg of the Co-dppe catalystin pH 6.8 phosphate buffer show a catalytic wave beginning near 1.25 Vvs. NHE when compared to a naked FTO electrode control. Thecharacteristics of the catalytic waves for catalysts formed with variedbidentate phosphines are, suggesting that the identity of the liganddoes play a role in the activity of the nanoparticles formed afterheating.

Tafel plots of catalytic currents in neutral conditions (5 differentelectrolytes, pH 7) show that this catalyst is active inproton-accepting media, suggesting a similar catalytic mechanism asNocera's catalyst. However, electrochemically three importantdistinctions arise when comparing these materials: first, this Co-dppecatalyst does not noticeably degrade in buffers that are poorproton-acceptors reducing the need for a consistently buffered aqueoussolution. Second, this catalyst is capable of sustaining current andwater oxidation through high applied potentials, specifically in aborate buffer. No appreciable degradation of the catalyst was found in apH 7 borate buffered solution after 12 hours with currents over 6mA/cm². Third, Co-dppe is more active in borate electrolyte than inphosphate, whereas the opposite trend is true for Nocera's catalyst—itis less active in borate than in phosphate.

The intimate incorporation and lack of decomposition of the phosphinesuggests that careful selection of ligand may allow for the tuning ofthe physical and chemical properties of material. Indeed materialsproduced by the same procedure, but with other bidentate phosphines,appear to be structurally similar to the Co-dppe catalyst, but displaydifferent activities as water oxidation catalysts. The shape of thecatalytic waves for catalysts formed with varied bidentate phosphinesare different, suggesting that the identity of the ligand does play arole in the morphology and catalytic activity of the nanoparticlesformed after heating. The highest activity was observed in samplesprepared using dppe. The robustness of this catalyst at high currents inproton accepting buffers and enhanced stability in buffers that are poorproton acceptors was attributed to the presence of a carbon backbone,present in SEM EDX, TEM EDX, and XPS of these materials.

The compositional and structural information obtained clearly indicatethat the Co-dppe catalyst is not a simple cobalt oxide. These data donot strictly exclude the possibility that the activity is attributableto impurities of such compounds. However, comparison of the activityprofiles of the Co-dppe catalyst with other known cobalt-based catalystssuggests that this is highly unlikely. Co₃O₄ is known to besignificantly less active at neutral and acidic pH, than under basicconditions; however, the Co-dppe catalyst maintains activity in bothneutral and strongly basic pHs. Co₃O₄ is also known to be unselectivefor the oxidation of water over the oxidation of chloride; however,—theCo-dppe catalyst is highly selective for the oxidation of water in thepresence of high concentrations of chloride. Nocera's catalyst wasreported to be unstable in solutions not containing significantconcentrations of phosphate or at high applied potentials; however,chronoamperograms of the Co-dppe catalyst show stability in sulfate atmodest overpotentials and borate at much higher potentials. Finally,whereas Nocera's catalyst is more active in phosphate than in borate,the Co-dppe catalyst is more active in borate than in phosphate.

IV. Methods of Use

The catalysts described herein can be incorporated into theoxygen-producing anode of a variety of devices for purposes including,but not limited to, splitting water by electrolysis to produce hydrogenat the cathode, splitting water by electrolysis to produce oxygen at theanode, electrochemical oxidation of organic species at the anode,reducing metal ions to their corresponding metallic neutral state at thecathode, reduction of organic species by electrolysis at the cathode,reduction of any other species at the cathode, as long as it is coupledwith oxygen production at the anode, and combinations thereof. Theseelectrolytic processes can be driven by a variety of energy sources,such as solar, wind, and/or nuclear.

The catalysts described herein can also be incorporated into theoxygen-consuming cathode of a variety of devices including, but notlimited to, oxygen-scavenging devices, oxygen-detectors, and fuel cellsor batteries which consume oxygen (pure, or in mixtures, such as air, orspecialty gas mixtures) in addition to any fuel including, but notlimited to, hydrogen, organic fuels, metallic fuels, or inorganic fuels.

The catalysts described herein can also be used in conjunction with achemical oxidant for the oxidation of organic species for synthetic ordestructive purposes.

A. Water Oxidation

The water oxidation catalysts (WOCs) described herein can be used in avariety of devices. In one embodiment, the device is a cell containingan anode and a cathode. Water is oxidized at the anode in the presenceof the WOC and hydrogen gas is evolved at the cathode. In someembodiments, the cathode contains a hydrogen evolution catalyst, forexample, coated on the cathode surface. Suitable hydrogen evolutioncatalysts include, but are not limited to, tungsten disulfide,molybdenum disulfide, cobalt tetraimines, cyclopentadienylruthenium-nickel catalysts, samarium hydroxide, colloidal platinumcatalysts stabilized by polyvinyl alcohol, dinuclear iron complexes,which are structural models of the active site of a type of enzyme (ironhydrogenases) which are efficient catalysts for hydrogen evolution,macrocyclic cobalt and nickel complexes, noble metals, and noble metaloxides and sulfides. Other hydrogen evolution catalysts are known in theart.

In other embodiments, water is oxidized at the anode, and metal ions arereduced to metals (Zn²⁺→Zn or Cu⁺→Cu etc.) at the cathode. In someembodiments the metal is deposited as a coating on the cathode(electroplating, electrogalvanization), and in other embodiments themetal is deposited on the cathode as crystals, powder, foam or nodules,which may be removed from the cathode.

The anode and cathode can be made from materials known in the art. Suchcells are known in the art and can be designed to conduct the reactionon any scale, including industrial scale. Alternatively, the reactioncan be conducted in a cell in which the anode is irradiated with lightresulting in the evolution of oxygen gas.

In still another embodiment, the reaction can be take place in thepresence of a supramolecular system, such as a nanomaterial ornanostructure. Such systems can be used to imitate photosynthesis byconducting both water oxidation and proton reduction in the samemolecular system. For example, in one embodiment, water is oxidized, inthe presence of a WOC, at one end or part of a nanomaterial ornanostructure to produce oxygen, hydrogen ions, and electrons. Theelectrons are transported rapidly to another part of the nanomaterial ornanostructure, where a water reduction catalyst (hydrogen evolutioncatalyst) catalyzes the reduction of hydrogen ions by electrons to formhydrogen gas.

Supramolecular systems include molecular assemblies and compositematerials. Exemplary materials include inorganic materials, such as highperformance semiconducting nanomaterials and hierarchically assemblednanostructures. The materials can be designed to enhance lightabsorption, for example, by the incorporation of molecular antennae.Inorganic-organic hybrid materials with enhanced light absorption andtunable bandgaps can be used as platforms for the catalysts describedherein. Other materials include nanotubes, nanosheets, etc., such asthose prepared from TiO₂, other inorganic materials, and organicmaterials. Molecular assemblies can be prepared from polymers andpolypeptides. Exemplary structures include polymer and coiled-coilpolypeptide assemblies that can precisely position molecular subunits inthree dimensions. Light harvesting assemblies prepared from polymers,such as one dimensional polymers, that absorb sunlight and efficientlytransport the excited state energy over long distances can also be used.Finally, printing technology can be used to design, fabricate, and testnanostructured metal-oxide electrodes for improved light capture insolar fuel devices.

The hydrogen gas produced in the device described above can be separatedfrom the oxygen gas. The hydrogen gas can be captured and stored untiluse. Alternatively, the devices described above can be linked to ahydrogen fuel cell or combustion reactor so that the hydrogen gas is feddirectly into the end device. The product of hydrogencombustion/hydrogen consumption is water. This water can be recycled andreoxidized using the catalysts and methods of use described herein.Oxygen is also produced in the catalytic reaction. Oxygen can be captureand stored and used for a variety of applications which oxygenproduction is desirable.

The catalysts described herein can be incorporated into one or more ofthe devices discussed above or other devices suitable for wateroxidation and the devices sold to the end user. Alternatively, thecatalysts described herein can be provided in a kit. The kits containsthe catalyst in a container, along with instructions for use of thecatalyst, and the end user incorporates the catalyst into one of thedevices discussed above or another device useful for water oxidation.For industrial scale processes, the amount of catalyst to be used canvary from milligrams to grams to kilograms to tons. One of ordinaryskill can readily determine the amount of catalyst need for a particularapplication on a particular scale.

For water oxidation, the minimum overpotential required for sustainingcurrent greater than 1 mA/cm² for the catalysts described herein isabout 400 mV at pH 7. While this value is higher than that exhibited byNocera's catalyst (e.g., 380 mV), Nocera's catalyst degrades atoverpotentials of 480 mV or greater while the catalysts described hereinare stable and continue to be active at overpotentials greater than 780mV. The buffers that can be used with the catalysts described herein aresignificantly less expensive than the buffers required for Nocera'scatalyst.

B. Electrochemical Fuel Cells

A fuel cell is generally an electrochemical cell that converts a sourcefuel into an electrical current and water. It generates electricityinside a cell through reactions between a fuel and an oxidant, triggeredin the presence of an electrolyte. The reactants flow into the cell, andthe reaction products flow out of it, while the electrolyte remainswithin it. Fuel cells can operate virtually continuously as long as thenecessary flows are maintained.

Fuel cells are different from conventional electrochemical cellbatteries in that they consume reactant from an external source, whichmust be replenished, a system known as a thermodynamically open system Ahydrogen fuel cell uses hydrogen as its fuel and oxygen (usually fromair) as its oxidant. Other oxidants, such as chlorine or chlorinedioxide can also be used. Examples of hydrogen fuel cells include, butare not limited to, proton exchange fuel cells, solid oxide fuel cells,and molten carbonate fuel cells.

Applications of hydrogen fuel cells include power sources forautomobiles and other vehicles, such as industrial equipment and powersources for remote locations, such as remote weather stations, largeparks, rural locations, and in certain military applications. Hydrogenfuel cells can also be used to power small electronic devices where ACcharging may not be available for weeks at a time, such as notebookcomputers, portable charging docks for small electronics (e.g. a beltclip that charges your cell phone or PDA), smartphones, GPS units, andsmall heating appliances. A fuel cell system running on hydrogen can becompact and lightweight, and have no major moving parts. Because fuelcells have no moving parts and do not involve combustion, they have highreliability, resulting in minimum down time.

D. Oxidation of Organic Compounds

The catalysts detailed herein can be used for the synthesis of commodityand specialty chemicals that are made by oxidation of precursor organicspecies possessing C—H bonds. This can be as a single step of amulti-step synthesis to form a complex product, as a stand-alonecatalytic reaction to transform one chemical into another singlechemical or group of chemical products, or to oxidatively degradeharmful or unwanted organic compounds to less harmful compounds such asacetate, formate, carbonate, and/or carbon dioxide. Oxidants that can beused with this catalyst include, but are not limited to, electrochemicaloxidants (an applied electric potential), chemical oxidants including,but not limited to, Oxone, potassium hydrogen peroxysulfate (KHSO₅),hydrogen peroxide, oxygen, ozone, or a combination of chemical andelectrochemical oxidants.

Applications of carbon-hydrogen bond oxidation using this catalystinclude bulk commodity chemical synthesis, remediation of organic waste,and synthesis of specialty chemicals due to selective oxidation ofspecific carbon-hydrogen bonds in an organic species.

EXAMPLES Materials

Commercially available xylenes (J. T. Baker, A.C.S. Reagent grade),1,2-bis(diphenylphosphino)ethane (Aldrich, 97%), Xantphos (Strem), 2,2%bis(diphenylphosphino)diphenyl ether (Aldrich), nitric acid (BDH,67-70%, trace metals analysis grade), sulfuric acid (J. T. Baker, 96%,ACS Reagent Grade), potassium phosphate monobasic (Sigma LifeScience, >99.0%), hydrogen peroxide (J. T. Baker, 30%, A.C.S. Reagentgrade), potassium nitrate (Acros Organics, A.C.S. Reagent grade), sodiumsulfate (Aldrich, A.C.S. Reagent grade), sodium acetate (Aldrich, A.C.S.Reagent grade), sodium tetraborate decahydrate (borax, Mallinckrodt,A.C.S. Reagent grade), boric acid, and potassium hydroxide (J. T. Baker,ACS Reagent Grade) were used as received.

Dicoablt octocarbonyl (Strem, stabilized with 1-5% hexane) could be usedas received, but required recrystallization from pentane after longperiods (acceptable if bright orange or red, but no darker).

Potassium bromide (Acros Organics, 99+%, spectroscopic grade), was driedover an open flame in a Schlenck flask under vacuum immediately prior touse.

Example 1. Catalyst Synthesis

In a nitrogen-filled glovebox, a 25×150 mm threaded Pyrex test tube wascharged with dicobalt octocarbonyl (345 mg, 1.01 mmol),1,2-bis(diphenylphosphino)ethane (399 mg, 1.00 mmol) and a largeTeflon-coated magnetic stirbar, and sealed with a Teflon screw-cap witha small silicone septum. The tube was suspended over a rapidly rotatingmagnetic stir plate, and xylenes (5.0 mL, freshly sparged with drynitrogen for 30 minutes) were added in one portion by syringe (immediateand rapid evolution of carbon monoxide was observed).

The mixture was stirred at ambient temperature until effervescenceceased (24° C., ca. 5 minutes). The tube was evacuated briefly andrefilled with dry nitrogen. The tube was inserted 2 cm deep into a 160°C. stirring polyethylene glycol bath. The reaction mixture rapidlyreached a stable reflux and was stirred vigorously for 90 minutes atreflux. Stirring continued as the mixture was allowed to cool to ambienttemperature, whereupon the cap was removed and the mixture was stirredopen to the atmosphere for 65 hours.

The reaction mixture was split evenly and transferred to two centrifugevials with ethyl acetate (8.0 mL final volume in each tube). The tubeswere centrifuged at 5000 rpm for 10 minutes, the dark supernatant wasremoved from the pale tan precipitate, and fresh ethyl acetate was added(8.0 mL). This process was repeated until the supernatant was colorless,and then once more without adding more solvent (6 centrifugation total).Drying under vacuum afforded the product catalyst (428 mg) as afree-flowing light tan to grey powder.

Mass Balance Studies

Trials were conducted in triplicate (precise data in table below). SmallTeflon-coated stirbars were placed in glass vials (9×85 mm, Exetainer®by Labco Limited), and their combined mass recorded (open to air). Thevials were brought into a nitrogen-filled glovebox and were charged withca. 100 μmol each of Co₂(CO)₈ (freshly recrystallized from pentane) anddppe. The vials were then each sealed with a threaded cap with aTeflon/rubber layered septum, and removed from the glovebox. Xylenes(800 μL, freshly sparged with dry nitrogen for 30 minutes) was added bysyringe, and the resulting mixture was stirred at ambient temperaturefor 5 minutes, before being inserted into a 2 cm deep aluminum heatingblock, and stirred for 1.5 hours at 160° C. The vials were then removedand allowed to cool to ambient temperature. Volatiles were removed byvacuum, and the contents were dried for 15 hours at ambient temperatureand <1 Torr. The caps were removed, and the precise mass of each vial,including stirbar and solid products, was determined (open to air).Xylenes (800 μL) was added to each vial by syringe, and the resultingmixtures were stirred open to the atmosphere for 65 hours at ambienttemperature. Volatiles were removed by vacuum, and the contents weredried for 15 hours at ambient temperature and <1 Torr. The caps wereremoved, and the precise mass of each vial, including stirbar and solidproducts, was determined (open to air). A summary of the data is shownin Table 2.

TABLE 2 Summary of mass balance data Trial A B C Mass of vial + stirbar11.446 g 11.7645 g 11.8234 g Mass of Co₂(CO)₈ 34.0 mg 36.7 mg 34.5 mg99.4 μmol 107.3 μmol 100.9 μmol Mass of dppe 39.6 mg 42.5 mg 40.5 mg99.4 μmol 106.7 μmol 101.7 μmol Δ Mass for −15.1 mg −17.7 mg −21.4 mgthermolysis −20.5%^(a) −22.3%^(a) −28.5%^(a) 539 μmol CO^(b) 632 μmolCO^(b) 764 μmol CO^(b) 5.4 equiv. CO^(c) 5.9 equiv. CO^(c) 7.6 equiv.CO^(c) Δ Mass for aeration +2.7 mg +3.3 mg +6.6 mg +3.7% +4.2% +8.8% ΔMass total −12.4 mg −14.4 mg −14.8 mg −18.8% −18.2% −19.7% ^(a)% = 100 ×(Δ Mass)/([mass Co₂(CO)₈] + [mass dppe]). ^(b)Assuming all mass lost isreleased CO. ^(c)Making previous assumption, and calculating based onmoles of Co₂(CO)₈.

Characterization of Catalyst

Microscopy/EDX

High resolution transmission electron microscopy (TEM) and energydispersive x-ray spectroscopy in the TEM (TEM-EDX) were used todetermine particle size, crystallinity (or lack thereof), and elementalcomposition with an FEI Tecnai Osiris TEM operating at 200 kV. TEMimages and TEM-EDX spectra were taken using silicon monoxide coated TEMgrids (Ted Pella, Product #01829) in order to monitor carbon content inthe as-synthesized material. For studies of sample alteration afterprolonged electrolysis in different electrolytes, scanning electronmicroscope (SEM) images and SEM-EDX spectra of the as-deposited andpost-electrolysis electrodes were taken using the electrode preparationprocedure described below and a Hitachi SU-70 SEM.

X-Ray Diffraction

Powder samples of 1, dppe and dppeO2 were subjected to 1.5418 Åradiation using a Bruker aXS D8 Focus spectrometer with a Cu source (40mA, 40 kV), with a stationary sample holder. The spectra below wererecorded using a 0.02° increment and 5 or 10 second exposure time perdata point.

The diffraction pattern of dppeO2 and that observed in samples ofCo-dppe are very similar, but not identical. The peaks are shown inTable 3.

TABLE 3 Peak locations Co-dppe dppeO₂ dppeO₂ (continued) 7.78 6.98 19.1811.04 7.74 19.78 11.52* 9.94 20.94 15.54 11.04 21.90 17.10 15.40 22.1823.40* 16.09* 23.30* 24.30 16.28* 24.30 17.06 25.00

The signal-to-noise apparent in the spectra of Co-dppe suggests thatonly a very small proportion of the sample is crystalline. These datacould indicate minor contamination with crystallites of Co-dppe, whichare a different crystalline phase than that observed for the purecompound.

ICP-MS

Before analysis, the catalyst was digested according to a modificationof a published procedure. A sample of the catalyst (11.5 mg) wascombined with 1.00 mL nitric acid (70%, trace metals analysis grade) ina vial, which was sealed with a plastic screw-cap containing aTeflon-lined septum. The mixture was heated in a 100° C. oil bath for 30minutes and allowed to cool to ambient temperature. Aqueous hydrogenperoxide (1.00 mL, 30%) was added to the mixture, and the mixture washeated in a 100° C. oil bath for 30 minutes (the vial was vented with a20 G needle for 3 seconds, to relieve excess pressure, after 3 minutesof heating). The mixture became turbid upon cooling to ambienttemperature, so another portion of aqueous hydrogen peroxide (1.00 mL,30% was added), and the mixture was heated in a 100° C. oil bath for anadditional 30 minutes. The resulting solution remained homogeneous uponcooling to ambient temperature, and even when immersed in a 0° C. icebath for 20 minutes.

The resulting solution was diluted to 25.00 mL with nanopure water in avolumetric flask. A 500 μL aliquot was diluted to 50.0 mL with 2.0%nitric acid (trace metals analysis grade), and subjected to analysis.This solution was found to contain 405 μg/L ³¹P and 771 μg/L ⁵⁹Co, whichindicates 1 is comprised of 8.710% P, w/w, 16.797% Co (1:0.987 P/Comolar ratio). A summary of the data is shown in Table 4.

TABLE 4 Summary of elemental analysis P-31 Co-59 Ru-101 Rh-103 Ir-191Pt-194 Sample (ppb) (ppb) (ppb) (ppb) (ppb) (ppb) 1 405 771 0.000260.00070 0.00094 0.00000 2 405 787 0.00000 0.00062 0.00026 0.00000 3 392760 0.00008 0.00043 0.00058 0.00000 Average 401 773 0.00028 0.000580.00059 0.00000

Elemental Analysis Combustion elemental analyses were conducted induplicate by Robertson Microlit, using an additional oxidant. Theresults are displayed in the

TABLE 5 Elemental analysis of C, H, and N Sample C H N 1 45.39% 3.94%<0.02% 2 45.18% 4.00% <0.02%

Temperature Programmed Desorption:

A U-shaped quartz tube (5×30 mm) was charged with 1 (2.8 mg). A constantflow of dry helium (50 mL/min) was used to purge the tube for 10minutes, and maintained throughout the experiment. A small, butconsistent percentage of the exhaust flow was diverted to a massspectrometer (Stanford Research Systems RGA100, employing anelectron-impact ionizer, a quadrupole mass filter and a Faraday cup iondetector) over the course of the experiment, and the masses of H₂O(m/z=18), CO (m/z=28), and CO₂ (m/z=44) were monitored. After adequatepurging, the quartz tube was inserted into a programmable heatingchamber, heated at a rate of 10° C./min. to 100° C., held constant at100° C. for 10 minutes, and then heated at a rate of 10° C./min to 890°C.

By the time the sample reached 300° C. it had lost H₂O, CO, and CO₂ in a3.19:1.91:1 molar ratio (3.73 μmol/mg (6.7% w/w), 2.23 μmol/mg (6.2%)and 1.17 μmol/mg (5.2%), respectively) (calibrated with calcium oxalate,monohydrate, which releases the gases in a strict 1:1:1 molar ratio).

Destructive Distillation

As shown in FIG. 1, 16×150 mm test tube 10 was charged with 27.1 mg ofcatalyst 12 and sealed with a rubber septum 14. The septum 14 waspierced with a 22 G needle, and connected to a vacuum line 16 (pressure<1 Torr throughout distillation). The base 75 mm of the tube was heatedto 250° C. 20 in a kugelrohr furnace 18. The other half of the tube wascooled in a stream of liquid nitrogen 22, which was expelled from aplastic wash bottle 24. After 2 hours subjected to these conditions, thetube was brought into a nitrogen-filled glovebox. The lower portion ofthe tube, containing the residue was cut off. The portion of the tubecontaining the sublimate was washed into a flask using dichloromethane.

After concentration under vacuum, the sublimate was dissolved in CDCl₃and identified as dppe by NMR. The amount was determined to be 220.0μmol by integration against an internal standard. This accounts for32.4% of the mass of added 1 (% of the ligand expected to be containedin 27.1 mg of 1).

Solubility Studies

Aliquots of the catalyst (3-8 mg) were combined with 1.0 mL quantitiesof the following solvents: acetonitrile, chloroform, dimethyl carbonate,dimethylformamide, dimethylsulfoxide, 1,2-dimethoxyethane, ethylacetate, ethylene glycol, methanol, nitromethane, pyridine,triethylamine and water. Even after prolonged stirring and sonication,no detectable ³¹P signal was found in any of the supernatants.

Solid State NMR

The MAS NMR was run on 500 MHz wide-bore Varian NOVA spectrometer with a9.5 mm Chemagnetics MAS probe spinning at 3.5 kHz. The magic angle wasadjusted with KBr, and the 31P chemical shift was referenced to liquidphosphoric acid, taken as 0 PPM. The pulse width was 30 degrees, therelaxation delay was 60 seconds, and the number of scans was 1260. Totalacquisition time was 21 hours.

As the MAS speed was low compared with the very broad 31P chemical shifttensor, we observed a lot of rotational sidebands. Because of limited 1Hdecoupling power, the center line of the ³¹P spectrum was also verybroad, around 1.5 kHz. In order to determine the isotropic chemicalshift, we ran another experiment with 3 kHz MAS. Comparing these twodata sets, we assigned 32 ppm as the isotropic chemical shift position.As the center peak was very broad, we were not able determine how manyisotropic peaks are present.

IR

Spectroscopy grade KBr (112 mg, anhydrous) and 1 (2.4 mg) were mixedtogether and cast into a pellet using a die and a hydraulic press (2000psi applied). The pellet was then analyzed with a Midac M1200spectrometer, purged with a constant flow of dry nitrogen gas (2ml/min.).

Electrochemistry

Deposition

A suspension of 1 in ethyl acetate (100 μL EtOAc per mg of 1) wasprepared by sonication (60 seconds, Branson 2510). 100 μL/in.² of thesuspension was then spread evenly over the surface of a FTO-coated glassslide (TEC 7, 1×1 in, 2.2 m thickness, Hartford Glass Co. Inc.). Theelectrode was allowed to dry in air for at least 20 minutes before beingcut in half From these electrodes 1 cm×1 cm active areas were cut outand measured to ensure an accurate calculation of geometric surfacearea. The electrode was immersed in an electrochemical cell andelectrochemical measurements were taken with a Princeton AppliedResearch Versastat 4-400 potentiostat/galvanostat using a standard threeelectrode set-up, with the sample as the working electrode, a platinumwire as the counter electrode, and an Ag/AgCl reference (BioanalyticalSystems, Inc., NHE vs. Ag/AgCl: +197 mV). All experiments were performedwithout IR compensation using 0.1 M buffer at pH 7, unless statedotherwise.

CVs

Cyclic voltammograms were used to determine performance of catalyticmaterials made using different organophosphine ligands. To ensure thatthe samples were stable throughout the CV, samples were equilibrated at1.2 V vs. Ag/AgCl for 4 minutes beforehand and no major increase ordecrease in current was observed. Below are CVs for cobalt-phosphinematerials made with four different organophosphines, with blue, red,black and green denoting dppe, Xantphos, triphenylphosphine, andDPEphos, respectively. Scan rate: 10 mV/s, 0.1 M potassium phosphate, pH6.8, no IR compensation, Pt wire counter electrode, Ag/AgCl reference,solution was gently stirred to assist mass transport of O₂ bubbles. Theresults are shown in FIG. 2.

Tafel Plots

Co-DPPE samples were tested for current stability prior to collection ofTafel plot data. Samples in nitrate, sulfate, and acetate did notexperience an increase or decrease in current over 10 minutes at 1.2 Vvs. Ag/AgCl. Phosphate buffer caused a slight decrease in current, whichwe attribute to replacement of phosphine by PO₄ ²⁻. Samples in boratebuffers showed a steady increase in current which lasted approximately 1hour, and were allowed to stabilize before obtaining Tafel plot data.This was attributed to incorporation of borate into the catalyst. Unlikepreviously discovered Co—Bi catalysts, however, we still seespectroscopic evidence of phosphorus (from dppe) in EDX spectra after >2hours of water oxidation at 1.4 V vs. Ag/AgCl suggesting that it plays arole in this catalyst's enhanced stability compared to other Co—Bimaterials. Tafel plots were taken while the solution was stirred at 25mV steps between 0.75 V vs. Ag/AgCl and 1.4 V vs. Ag/AgCl with a 10second rest time between data points. After initial spikes in currentcaused from capacitance, steady-state values were attained withinapproximately 2 minutes and plotted in FIG. 3.

Electrochemistry in basic conditions was performed using an FTOelectrode with a catalyst surface loading of 0.42 mg/cm², and 0.10 MNaOH. After equilibration (10 minutes, 0.80 V vs Ag/AgCl), the Tafelplot was taken at 25 mV steps between 0.360 and 1.210 V vs Ag/AgCl witha 5 second rest time between data points. Amperometric data was recordedfor 5 minutes at each potential, and values for the last 2.5 minuteswere averaged to afford the value included in the Tafel plot. Theresults are shown in FIG. 4. The slope of the linear region is 63mV/decade.

Oxygen detection was performed with a TauTheta MFPF-100 KHz using phasefluorometry (calibrated with argon [Tech Air] and air). A 250 mLthree-neck round bottom flask was charged with 0.1 M borate electrolyte(leaving ca. 60 mL headspace). A large, Teflon-coated stirbar was usedto agitate the electrolyte gently. The flask was thermostated at 25° C.A reference electrode (Ag/AgCl), the working electrode, and a Pt wirecounter electrode were each inserted through large rubber septa, and theoxygen detector was inserted through the rubber septum with the anode.The septa were then inserted into the necks of the flask such that theelectrodes were all submerged and tip of the fluorescence probe was ca.3 cm above the surface of the electrolyte.

Once assembled, the septa were secured with Parafilm® and electricaltape. The flask was purged with argon (which was bubbled through theelectrolyte, not just the headspace) until the oxygen level reached astable minimum. The purge was ceased, and the oxygen level monitored for30 minutes to be sure that there was no leakage. A constant potential of1.4 V vs the Ag/AgCl reference electrode was then applied for 60minutes, and oxygen detection was maintained until oxygen levels reacheda stable maximum. The headspace volume was determined to be 55.0 mL atthe end of the experiment.

Stability Studies and Post-Electrolysis Analyses

Chronoamperograms at varied potentials for one hour in sulfate, borate,and phosphate buffers were performed using the conditions outlinedabove. No decay in current or of the catalyst deposited on the FTOelectrode was seen for any applied potential in a borate buffer. Insulfate, no decrease in current or degradation of catalyst was seen at1.1 V vs. Ag/AgCl (1.3 V vs. NHE) or 1.2 V vs. Ag/AgCl (1.4 V vs. NHE),while a slight decrease in current can be seen at 1.3 V vs. Ag/AgCl (1.5V vs. NHE) and finally a significant decrease in current and degradationof catalyst at 1.4 V vs. Ag/AgCl (1.6 V vs. NHE). In phosphate,chronoamperograms show stable current at 1.1 V vs. Ag/AgCl (1.3 V vs.NHE), however at all higher potentials there is a slow degradation ofcurrent observed as shown in FIG. 5.

After 2 hours of electrolysis at 1.4 V vs, Ag/AgCl (1.6 V vs. NHE), theCo-dppe retains phosphorus as shown by SEM-EDX. Similar retention ofphosphorus is seen in sulfate buffered samples after 2 hours ofelectrolysis.

Long-term stability studies were performed in a two-compartmentelectrochemical cell with each compartment separated by a glass frit. 12hour uninterrupted stability at 1.4 V vs. Ag/AgCl was investigated. Theresults show that after over 40 hours of intermittent use at variedpotentials between 1.1 V vs. Ag/AgCl and 1.4 V vs. Ag/AgCl high activityis still retained. See FIGS. 6A-B.

While electrolysis in borate appears to cause a change in the catalyst,it is reversible. Upon immersing a sample in a sulfate buffered solutionafter 12 h of electrolysis in a borate buffered solution, its prioractivity is retained. See FIG. 7.

XPS Analysis

FTO electrodes (one blank [A], one with fresh catalyst deposited on it[B], one with catalyst that had undergone >40 h electrolysis in borate[C], and one with catalyst that had undergone electrolysis in sulfate[D]) were sent to CAMCOR (at the University of Oregon) for XPS analysis.Spectra were taken on a ThermoScientific ESCALAB 250 instrument,employing monochromatized X-rays from an aluminum source. Pass energiesof 150 eV and 20 eV were used for survey and composition scans,respectively. In both cases a beam-width of 500 μm was used.

Loading Studies

Suspensions of 1 in ethyl acetate were prepared in the following manner:A 20 mL scintillation vial (A) was charged with 1 (2.4 mg) and ethylacetate (12.0 mL). Another vial (B) was charged with ethyl acetate (12.0mL). Vial A was sonicated briefly and well mixed just before a portion(1.00 mL) of the suspension was transferred to vial B. Portions of eachsuspension (500 μL) were thoroughly applied to FTO-electrodes (A and B),while a third electrode was treated with 500 μL of ethyl acetate only.After drying for 30 minutes, the electrodes were assessed bychronoamperometry at 1.6 V vs NHE in pH 7.0 0.1 M borate electrolyte.Current densities reported in Table 6 are averages of the currentdensity over the last five minutes of a 20-minute CA.

TABLE 6 Average current densities Electrode A B Blank μM 1/cm² 15.5 1.290 mA/cm² 0.540 0.538 0.018 Calculated moles 93 1120 NA of (O₂)/Co atom ·h

Differentiation from Co-Pi and Co₃O₄

Electrolysis was conducted in either 0.1 M borax at pH 7 or in 0.1 Mphosphate at pH 7. The working electrode was either: an FTO electrodeactivated with Co-Pi by the method published, 2 an FTO electrode withCo3O4 deposited on it, an FTO electrode with 1 deposited on it, or anFTO electrode with 1 deposited on it which had been run at 1.4 V vsAg/AgCl in 0.1 M borate for 12 h before beginning the experiment.Platinum mesh was used for the counterelectrode, and Ag/AgCl as thereference. Each of the plates was subjected to 6 consecutive 1 hchronoamperometry experiments at 1.40 V vs Ag/AgCl in alternating fresh20 mL electrolyte solutions (borate, then phosphate, then borate, thenphosphate etc.). All electrodes were rinsed with 18 MΩ deionized waterbefore introduction to the new electrolyte. The setup was such that thethree electrodes were always in the same position relative to eachother, to ensure minimal change in current due to resistivity. Thecurrents in the Table 7 are average values for the last 10 minutes ofeach hour-long run, which clearly demonstrate three different behaviors:Co-Pi, which is better in phosphate than in borate; Co₃O₄ which is worsein each successive run; and 1 which is better in borate than inphosphate.

TABLE 7 Average current values Co-Pi Co₃O₄ 1 1 after 12 hrs Borate 1.6mA 0.9 mA 1.7 mA 0.8 mA Phosphate 3.4 mA 0.7 mA 0.4 mA 0.5 mA Borate 1.6mA 0.6 mA 0.8 mA 0.7 mA Phosphate 3.2 mA 0.3 mA 0.3 mA 0.3 mA Borate 1.5mA 0.3 mA 0.7 mA 1.0 mA Phosphate 3.0 mA 0.3 mA 0.3 mA 0.2 mA

Example 2. Scaled Up Catalyst Synthesis

A 250 mL round-bottom flask equipped with a large Teflon-coated stirbarand a reflux condenser sealed with a rubber septum was filled with thynitrogen. The reflux condenser was removed, and dicobalt octacarbonyl(22.8 g) was added quickly, before replacing the condenser. The flaskwas purged with dry nitrogen for 15 minutes. Xylenes (50 mL, spargedwith nitrogen) was added by syringe and the reaction vessel was placedabove a magnetic stirplate. Once the dicobalt octacarbonyl was fullydissolved, a stream of dry nitrogen was passed through the headspace ofthe reaction flask and was vented through a bubbler. A suspension of1,2-bis(diphenylphosphino)ethane (26.4 g) in xylenes (110 mL, spargedwith nitrogen) was added quickly by cannula. Evolution of CO gas wasobserved. The reaction mixture was heated to 160° C. (reaching reflux)and stirred vigorously for one hour. The reaction vessel was allowed tocool for 30 minutes before the condenser was removed. The reactionmixture was stirred vigorously, open to the air, for 4 days. Theresulting heavy suspension was filtered using a Büchner funnel, andwashed with ethyl acetate until the filtrate was colorless. Theremaining brown powder was dried under vacuum, yielding the catalyst(22.0 g).

Stability in Strongly Basic Electrolytes

The catalysts described herein are stable in strongly basic electrolytes(e.g., pH 12 to 30 wt % KOH) for extended periods of time, for example,greater than two months.

The results are shown in FIG. 9. A suspension of Co-dppe was prepared inetheyl acetate (9.9 mg/mL), and sonicated for 20 seconds. 100 μL of thesuspension was applied to each side of a nickel electrode (28mm×12.5×0.127 mm), and allowed to air dry (about 5 minutes, each). Thiselectrode was used as the anode, in conjunction with cathode consistingof only nickel foil (28 mm×12.5×0.127 mm). Two nickel foil electrodes(28 mm×12.5×0.127 mm) were connected to a potentiostat as the counterelectrode (cathode) and reference electrode. The anode with catalystdeposited on it was attached as the working electrode (anode), separatedfrom the counter electrode and reference electrode by approximately 2.9cm each. Approximately 1.6 cm of each electrode was submerged in a 25 wt% solution of KOH in deionized water. Cyclic voltammetry from −1.20 to1.20 V vs the reference electrode was performed at 50 mV/second, at roomtemperature. An electrochemical setup identical to the first, butemploying an anode lacking catalyst (nickel foil only) was subjected tothe same conditions as a control. The results are shown in FIG. 9.

The system employing catalyst was shown to be more active than thecontrol: the system with catalyst achieved a current density of 0.01A/cm² at a potential 69 mV lower than the control, and 0.05 A/cm² 147 mVlower. The catalytic system achieved a current density between 75% and450% greater than the control system across the voltage range of 800 mVto 1200 mV. This experiment also demonstrated that the catalyst isstable under both oxidizing and reducing applied potentials (−1.2 to+1.2 V vs Ni foil in same electrolyte).

Example 3. Synthesis and Characterization of Related Catalysts

Inside a N₂ atmosphere glovebox, a stock solution of Co₂(CO)₈ wasprepared by weighing 975 mg into a Schlenk bomb and adding 39 mL of N2sparged xylenes. The ligands 1,2-ethanediylbis[diphenylphosphine oxide],DPEphos, triphenylphosphine, 1,2-Bis(1-piperidinyl)ethane, TMEDA, EDTA,4,4′-bipyridine, 2,2′-bipyridine, dppm, dppe, dppb, and dppp wereweighed out into reaction tubes in an equimolar ratio to the Co₂(CO)₈(except PPh₃ 2 mol eq). The tubes were sealed, evacuated and refilledwith N₂ three times.

Under nitrogen, 3 mL of the cobalt solution was added to each tube. Thereactions were allowed to stir for 30 min under nitrogen purge. Thetubes were heated to 160° C. for 90 min. The reactions were cooled toroom temperature and allowed to stir open to air for 36 hrs. Thereactions were centrifuged down and decanted. The solids were washedwith ethyl acetate, centrifuged, and decanted until the solution wasstill clear after separation. The resulting solids were dried on highvacuum. IR spectra were recorded for each material.

Approximately 1 mg of each material was suspended in 250 μL of ethylacetate by sonicating and then drop casting onto fresh FTO electrodes.The electrodes were allowed to dry overnight before electrochemicalmeasurements were made. The electrochemical measurements were carriedout in a small beaker with 40 mL 0.1 M borate electrolyte pH 7. AnAg/AgCl reference electrode was used along with platinum mesh as thecounter electrode. Each sample underwent a 1.2 V (vs Ag/AgCl) appliedpotential for 4 min prior to recording a CV for the material. A CV wasrecorded from 0.2 to 1.4 V at a scan rate of 10 mV/sec. The results areshown in FIGS. 10A-M.

Materials formed from CO₂(CO)₈ and dppe, (FIG. 10A),1,2-ethanediylbis[diphenylphosphine oxide] (FIG. 10B), DPEphos (FIG.10C), triphenylphosphine (FIG. 10D), 2,2′-bipyridine (FIG. 10E), TMEDAor EDTA (FIG. 10F), were found to be very active as water oxidationcatalysts. Materials formed from 1,2-Bis(1-piperidinyl)ethane (FIG.10G), dppm (FIG. 10H), dppb (FIG. 10I), dppp (FIG. 10J) andN¹,N^(1′),N²,N^(2′)-tetramethylethane-1,2-diamine (FIG. 10K) were foundto be somewhat active as water oxidation catalysts. The material formedfrom 4,4′-bipyridine (FIG. 10L) was found to be inactive as a wateroxidation catalyst, and formed non-conductive film on the electrode,ultimately deactivating it for water oxidation. FIG. 10L is a negativecontrol without catalyst.

Example 4. Electrolytic Production of Zinc from Alkaline Solutions ofZinc Oxide

Preparation of the “Activated Electrode”

A suspension of Co-dppe was prepared in etheyl acetate (9.9 mg/mL), andsonicated for 20 seconds. 100 μL of the suspension was applied to eachside of a nickel electrode (28 mm×12.5×0.127 mm), and allowed to air dry(about 5 minutes, each).

Preparation of the “30 g/L Zinc Electrolyte”

Zinc oxide (15.0 g) was dissolved in 500 mL of a pre-formed 25 wt %solution of sodium hydroxide in deionized water, resulting in ahomogeneous solution.

Preparation of the “Saturated Zinc Electrolyte”

Zinc oxide (20.0 g) was added to 150 mL of pre-formed “30 g/L ZincElectrolyte” and stirred vigorously overnight. The slurry was thenallowed to settle for 1 hour, and the milky suspension (the “SaturatedZinc Electrolyte”) was decanted from the majority of undissolved zincoxide.

Electrolysis 1 (Control with No Catalyst in “30 g/L Zinc Electrolyte”)

A PET beaker was filled with “30 g/L Zinc Electrolyte” (120 mL) Threenickel foil electrodes (28 mm×12.5×0.127 mm) were connected to apotentiostat as the working electrode (anode), counter electrode(cathode) and reference electrode. Approximately 1.6 cm of eachelectrode was submerged. Cyclic voltammetry from 0.5 to 1.40 V vs thereference electrode was performed at 5 mV/second at room temperature.(Hydrogen bubbles begin forming on the nickel cathode at 1.20 V on thefirst cycle, and from the zinc-coated cathode around 1.24 V thereafter).A constant voltage of 1.20 V vs the reference electrode was thenapplied, at room temperature, for 6 hours, inducing a current thatstarted at 3.4 mA/cm² and increased to 22.1 mA/cm² by the end(calculated based on submerged anode surface area which remainedconstant throughout electrolysis.)

Electrolysis 2 (with Catalyst in “30 g/L Zinc Electrolyte”)

A PET beaker was filled with “30 g/L Zinc Electrolyte” (120 mL). Twonickel foil electrodes (28 mm×12.5×0.127 mm) were connected to apotentiostat as the counter electrode (cathode) and reference electrode.An “Activated Electrode” was attached as the working electrode (anode).Approximately 1.6 cm of each electrode was submerged. Cyclic voltammetryfrom 0.5 to 1.40 V vs the reference electrode was performed at 5mV/second, at room temperature. A constant voltage of 1.20 V vs thereference electrode was applied, at room temperature, for 16 hours,inducing a current that started at 15.5 mA/cm² and increased to 44.4mA/cm² by hour 6, and up to 63.3 mA/cm² by the end (calculated based onsubmerged anode surface area which remained constant throughoutelectrolysis.) The “Activated Electrode” was removed and rinsed withdeionized water. The electrode was shown to remain activated for wateroxidation.

Electrolysis 3 (Control with No Catalyst in “Saturated ZincElectrolyte”)

A PET beaker was filled with “Saturated Zinc Electrolyte” (120 mL).Three nickel foil electrodes (28 mm×12.5×0.127 mm) were connected to apotentiostat as the working electrode (anode), counter electrode(cathode) and reference electrode. Approximately 1.6 cm of eachelectrode was submerged. Cyclic voltammetry from 0.5 to 1.40 V vs thereference electrode was performed at 5 mV/second at room temperature. Aconstant voltage of 1.20 V vs the reference electrode was applied, atroom temperature, for 60 seconds, inducing a current that started at 5.0mA/cm² and decreased to 3.3 mA/cm² by the end (calculated based onsubmerged anode surface area which remained constant throughoutelectrolysis.) A second constant voltage of 1.30 V vs the referenceelectrode was applied, at room temperature, for 120 seconds, inducing acurrent that started at 7.3 mA/cm² and decreased to 6.5 mA/cm² by theend (calculated based on submerged anode surface area which remainedconstant throughout electrolysis.)

Electrolysis 4 (with Catalyst in “Saturated Zinc Electrolyte”)

The setup described in “Electrolysis 3” was modified by replacing theworking electrode (anode) with the “Activated Electrode” used in“Electrolysis 2.” Cyclic voltammetry from 0.5 to 1.40 V vs the referenceelectrode was performed at 5 mV/second at room temperature. A constantvoltage of 1.20 V vs the reference electrode was applied, at roomtemperature, for 300 seconds, inducing a current that started at 21.2mA/cm² and remained constant (calculated based on submerged anodesurface area which remained constant throughout electrolysis.)

A second constant voltage of 1.30 V vs the reference electrode wasapplied, at room temperature, for two hours, inducing a current thatstarted at 37.5 mA/cm² and increased to 46.6 mA/cm² by the end(calculated based on submerged anode surface area which remainedconstant throughout electrolysis.)

A third constant voltage of 1.40 V vs the reference electrode wasapplied, at room temperature, for 45 minutes, inducing a current thatstarted at 63.1 mA/cm² and increased to 70.8 mA/cm² by the end(calculated based on submerged anode surface area which remainedconstant throughout electrolysis.)

A fourth constant voltage of 1.50 V vs the reference electrode wasapplied, at room temperature, for 300 seconds, inducing a current thatstarted at 87.9 mA/cm² and decreased to 85.3 mA/cm² by the end(calculated based on submerged anode surface area which remainedconstant throughout electrolysis.)

A fifth constant voltage of 2.20 V vs the reference electrode wasapplied, at room temperature, for 50 minutes, inducing a current thatstarted at 195.59 mA/cm2 and increased to 255.5 mA/cm2 by the end(calculated based on submerged anode surface area which remainedconstant throughout electrolysis.)

After these experiments, the “Activated Electrode” was removed andrinsed with deionized water. The electrode was shown to remain activatedfor water oxidation, and analysis by SEM and SEM/EDX showed the catalystwas still bound to the surface, morphologically unchanged and notcontaminated with any zinc.

The current density as a function of applied potential (V vs Ni) forcatalyst and no catalyst is shown in FIGS. 11A and B. The experimentcomparing nickel electrodes with and without catalyst in the electrolytesaturated with zinc oxide demonstrated that the catalyst significantlyincreased the activity, allowing a current density of 0.005 A/cm² at apotential 160 mV lower than the identical setup without catalyst, and acurrent of 0.01 A/cm² at a potential 195 mV lower. The cells withoutcatalyst have nearly identical performance in both high and lower zincconcentrations, while the cells with catalyst have significantly loweronset potential at higher zinc concentration. This indicates that thecathodic zinc reduction reaction is rate limiting in cases where theanode is activated with catalyst, while the anodic water oxidationreaction is rate limiting in cases without any catalyst. Theseexperiments also demonstrate stability of the catalyst in the presenceof high concentrations of zinc over extended periods of time.

Example 5. Hydrogen Electrolyzer Study

A dry-cell alkaline electrolyzer consisting of six stainless steelplates (two terminal plates and four bipolar plates), separated by 3-mmneoprene gaskets, was disassembled. A suspension of 224 mg Co-dppe in25.0 mL ethyl acetate was sonicated for 45 seconds. 4.0 mL portions ofthe suspension were applied to one face of each of the four bipolarplates, and both faces of one of the terminals. After air-drying, theseplates were reassembled such that the faces of the bipolar plates withcatalyst were directed at the terminal plate without catalyst (see FIG.16).

The electrolyzer was connected to a reservoir filled with 1N NaOHelectrolyte, and run at a constant current of 5.0 A for 50 days. Theelectrolyte level was maintained by adding deionized water ever 2 orthree days, as needed, and the electrolyzer was drained, rinsed andrefilled with new 1N NaOH every 7 to 12 days. After each refill, theelectrolyzer was subjected to a study in which the applied voltage wasadjusted between 8.1 and 14.5 V (1.62-2.9 V/cell). The current wasmeasured at each potential, and recorded. Another dry-cell alkalineelectrolyzer of the same dimensions, but without catalyst was filledwith the same electrolyte each time, and used as a control for eachstudy. The two electrolyzers are compared in FIGS. 12A-F over periods oftime of one day (12A), 13 days (12B), 20 days (12C), 34 days (12D), 42days (12E), and 50 days (12F).

This study shows that activation of the electrolytic cell improvesoutput by at least 20% (up to 100%) at a given voltage in the range ofnominal working conditions, and that this improvement is long-lived:surviving >50 days of continuous operation and at least 5 completeelectrolyte replacements and rinses of the cell.

Example 6. Electrochemical Oxidation of Glycerol

A solution of 0.9 M glyercerol and 1.1 M NaOH in D₂O was prepared aselectrolyte. An H-cell with a coarse glass frit separating the anodicand cathodic chambers was filled with the electrolyte (45 mL). An FTOelectrode with 680 mg 1 per cm² was used as the anode, a platinum meshwas used as the cathode, and a silver wire submerged in the anolyte wasused as the reference electrode. The voltage was adjusted to achieve thegreatest current without observing bubble formation (oxygen production)at the anode. A potential of 0.9 V (vs Ag wire reference) was found tobe optimal. After 72 hours, an aliquot of the anolyte was analyzed by¹HNMR (acetic acid added as internal standard for integration). Formatewas found to be the major product (89% Faradaic yield), with traces oflactic acid (˜1% Faradaic yield).

Example 7. Oxidation of Organic Compounds Using Chemical Oxidants

Oxidant Screens for C—H Oxidation

Sodium ethylbenzene sulfonate was used as a test substrate for C—Hoxidation. A variety of common oxidants were screened for activity withthe catalyst. Stock solutions of sodium ethylbenzene sulfonate and eachoxidant were prepared by adding degassed D₂O and the respective oxidantby syringe into tubes under N₂ atmosphere (if oxidant was solid it wasadded prior to flushing tubes with N₂). Reaction tubes with stirbars and1 mg of catalyst (e.g., Co-dppe) were evacuated under vacuum and flushedwith N₂ several times before adding stock solution of the sodiumethylbenzene sulfonate. The reactions were initiated by addition of thestock solution of oxidant. After 1 hour, a stock solution of d₄-sodiumtrimethylsilyl propionate (NMR internal standard) andd₆-dimethylsulfoxide (oxidant quench) in D₂O was added. The reactionsstirred another 15 min and then were filtered into NMR tubes. Thereaction yield was quantified by NMR using the internal standard.Reaction conditions: 20 μmol sodium ethylbenzene sulfonate, 100 μmoloxidant, 1 mg catalyst (e.g., Co-dppe), 500 μL D₂O; under N₂ at roomtemperature for 1 hr.

Oxone and its isolated active component, KHSO₅, were determined to bethe only oxidants that showed any appreciable activity for the oxidationof sodium ethylbenzene sulfonate under these conditions.

Terminal Entry Oxidant Product Yield 1 H₂O₂  0% 2 ^(t)BuOOH  0% 3 KHSO₅85% 4 Oxone 70% 5 NaIO₄  0% 6 NaIO₃  0% 7 mcpba  0% 8 K₂S₂O₈  0%Conditions: 20 umol EBS, 100 umol oxidant, 1 mg 1, 500 uL D₂O RT, 1 hrunder N₂; NMR yields determined by d₄-TMSP standard

Substrate Screen (Selective Oxidation)

Several substrates were screened for C—H oxidation using the catalyst(e.g., Co-dppe) and KHSO₅. The general conditions for the screen were:20 μmol sodium ethylbenzene sulfonate, 100 μmol oxidant, 1 mg catalyst(e.g., Co-dppe), 500 μL 4:1 d₆-acetone:D₂O; under N₂ at roomtemperature.

A stock solution of KHSO₅ was prepared in degassed D₂O under N₂.Catalyst (e.g., Co-dppe) was added to each reaction tube. The tubes werethen evacuated under vacuum and refilled with N₂ several times. 400 μLof d₆-acetone was added to each tube followed by the appropriatesubstrate. Reactions were initiated by the addition of 100 μL of KHSO₅stock solution. Reactions were monitored for 3 or 15 hrs depending onthe substrate. The reactions were quenched by addition of a stocksolution of d₄-sodium trimethylsilyl propionate (NMR internal standard)and d₆-dimethylsulfoxide (oxidant quench). The reactions stirred another15 min and then were filtered into NMR tubes. The reactions werequantified by NMR. (Control reactions were performed without catalystand in each case the substrate conversion is >5%)

For most of the substrates selective oxidation to a single product wasobserved. The catalyst system was able to oxidize unactivated alkanes toa single product but in low yield. Oxidation of 1-butanol illustratesthe difference the catalyst and simple cobalt salts. The catalystselectively oxidizes butanol to butyric acid whereas the Co(II) saltstested were highly unselective, affording several different products.

% Mass Rxn Substrate Major Product yield balance  1^(b) CyclohexaneCyclohexane 20  60  2^(b) Styrene 1-Phenyl-1,2-ethanediol 36  72  3^(a)THF γ-butyrolactone 42 >95  4^(a) Butanol Butyric acid 70 >95  5^(b)Cumene Acetophenone 31  79  6^(b) 2-hexanone Acetonylacetone 15  93 7^(b) Pyrrolidine 2-Pyrrolidine 95 >95  8^(b) Benzyl alcohol Benzoicacid 51  93  9^(b) Cyclopentanol Cyclopentanone 47  66 10^(b)Ethylbenzene 4-acetophenone sulfonate 90 >95 sulfonate 11^(b)D-sec-phenethyl Acetophenone 75 >95 alcohol 12^(b) Ethyl benzeneAcetophenone 46  85 ^(a)Reaction time 3 hrs ^(b)Reaction timer 15 hrs

Water Oxidation Vs Chemical C—H Oxidation

The vessel shown below was charged with 6 mg of catalyst (e.g., Co-dppe)and then evacuated under vacuum and refilled with nitrogen severaltimes. A stock solution of sodium ethylbenzene sulfonate in degassed D₂Owas added to the vessel. The oxygen concentration was monitored with aTauTheta MFPF-100 KHz using phase fluorometry (calibrated with argon[Tech Air] and air). The reaction was initiated by addition of stockKHSO₅ in degassed D₂O. The reaction was monitored for 1 hr after which astock solution of d₄-trimethylsilylpropionate and d₆-DMSO in D₂O wereadded. The reaction was stirred an additional 15 min then filtered intoan NMR tube for analysis. The C—H oxidation was quantified by protonNMR. The conditions were as follows: 120 μmol sodium ethylbenzenesulfonate, 600 μmol KHSO5, 6 mg catalyst (e.g., Co-dppe), and 3 mL D₂O.

After 1 hr 120 μmol of sodium acetophenone sulfonate and 2.7 μmol of O₂were measured. The system is highly selective for C—H oxidation overwater oxidation. Many catalysts that are capable of water oxidation areincapable of selective C—H oxidation over water oxidation. In thissystem, combination of the catalyst (e.g., Co-dppe) and oxidant seems tobe below the oxidation potential for water oxidation while still highenough to oxidize many types of C—H bonds.

Pollutant Remediation

The catalyst was used to attempt to mineralize common persistentenvironmental pollutants. Catalyst (e.g., Co-dppe) and substrates wereweighed into reaction tubes and 400 μL of d₆-acetone was added. Thereactions were initiated by addition of KHSO₅ in D₂O. Reactions werecarried out open to air at room temperature. A stock solution ofd₄-trimethylsilylpropionate and d₆-DMSO in D₂O were added. The reactionwas stirred an additional 15 min then filtered into an NMR tube foranalysis. NMR yields calculated by internal standard Conditions: 20 μmolsubstrate, 100 μmol oxidant, 1 mg catalyst (e.g., Co-dppe), 500 μL 4:1d₆-acetone:D₂O. The pollutants were dibenzodioxin, dibenzofuran, and1,4-dioxane, the structure of which are shown below:

% Yield % Major after 15 Reaction Substrate remaining product minutes 1Dibenzodioxin  62 N/A N/A 2 Dibenzofuran  42 Acetate 58 3 1,4-dioxane~10 Formate 50

Many environmental pollutants are persistent in the environment or aredifficult to treat due to their physical properties. The catalyst showedpotential for further study in the remediation of environmentalpollutants. The major products in two of the cases were benign acetateand formate.

Dye Bleaching Screen

Several different dyes were screened with the catalyst and KHSO₅ inwater. The reaction was monitored by measuring the relative absorbanceat λ_(max) for each dye. A stock suspension of the catalyst (e.g.,Co-dppe) was prepared in water. The suspension was thoroughly sonicatedjust prior to the experiment to ensure minimal aggregation. The stockdye and catalyst were added to a cuvette and the reaction was initiatedby addition of stock KHSO₅ in water. Conditions: 40 μM dye, 1.5 mMoxidant, variable cat; RT open atm; 1 mL unbuffered H2O; monitor abs atλmax; Dyes Basic Blue 24, Brilliant Blue G, Bromophenol Blue, BuffaloBlack, Methylene Green, Orange G. The structures of these dyes are shownbelow:

The results are shown in FIG. 13. The catalyst (e.g., Co-dppe) and KHSO₅system was able to bleach a wide range of structurally different dyes.In most case reaching 50% of the initial absorbance in ca. 5 min.

Catalyst Dependence: Dye Bleaching

The series of reactions were set up identical to the above experiment.Orange G was chosen as the model dye and the loading of catalyst wasvaried (ca. 0, 1.4, 3.5, 7, 10.4 nmol). Conditions: 40 μM Orange G dye,1.5 mM oxidant, variable cat; RT open atm; 1 mL unbuffered H₂O; monitorabs at λmax. The left over solution was centrifuged and decanted. To thedecanted solution was added another aliquot of dye and oxidant. Theresults are shown in FIG. 14. The resulting rate was significantlyslower than the initial rate but slightly faster than the rate of KHSO₅alone. This suggests that soluble Co(II) species are not the primarycatalyst for this reaction.

Despite the heterogenous nature of the catalyst the loading of thecatalyst affects rate of dye bleaching. The results are shown in FIG.15. The data shows that the catalyst is responsible for the rate of dyebleaching and not soluble Co(II) species.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meanings as commonly understood by one of skill in the artto which the disclosed invention belongs. Publications cited herein andthe materials for which they are cited are specifically incorporated byreference.

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, many equivalents to the specificembodiments of the invention described herein. Such equivalents areintended to be encompassed by the following claims.

We claim:
 1. A system comprising a substrate and a catalyst, wherein thecatalyst is in the form of a layer, coating, or particles bound to thesubstrate and retains its activity; wherein the substrate comprises ametal oxide, mixed-metal oxide, or combinations thereof and the metaloxide and/or mixed metal oxide is a conductive oxide; and wherein thecatalyst has the chemical formula:MY_(a)(CO)_(b)O_(c)(OH)_(d)(H₂O)_(e) wherein M is a d-block transitionmetal selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, Rh,Ir, and combinations thereof; Y is a bidentate ligand; a is any valuefrom about 0.5 to about 1; b is any value from about 0 to about 3; c isany value from about 1.5 to about 3; and d is any value from about 0 toabout 4; and e is any value from about 0 to about
 6. 2. The system ofclaim 1, wherein the M is cobalt.
 3. The system of claim 1, wherein theM is nickel.
 4. The system of claim 1, wherein the M is chromium.
 5. Thesystem of claim 1, wherein the M is copper.
 6. The system claim 1,wherein the M is iron.
 7. The system of claim 1, wherein the M ismanganese.
 8. The system of claim 1, wherein the M is rhodium.
 9. Thesystem of claim 1, wherein the M is iridium.
 10. The system of claim 1,wherein b is from about 0 to about
 2. 11. The system of claim 1, whereinthe Y is charged.
 12. The system of claim 1, wherein the Y is uncharged.13. The system of claim 12, wherein the Y is a phosphorous-based ligand.14. The system of claim 13, wherein the phosphorus-based ligand isselected from the group consisting of diallyl phosphines, trialkylphosphine, alkyl diaryl phosphines, triaryl phosphines, and combinationsthereof.
 15. The system of claim 14, wherein the phosphorus-based ligandis an alkyl diaryl phosphine.
 16. The system of claim 13, wherein thephosphorus-based ligand is selected from the group consisting of dppe,Xantphos, DPEphos, 1,2-ethanediylbis[diphenylphosphine oxide], andcombinations thereof.
 17. The system of claim 12, wherein the ligand isa nitrogen-based ligand.
 18. The system of claim 17, wherein thenitrogen-based ligand is a N-heterocycle.
 19. The system of claim 17,wherein the nitrogen-based ligand is selected from the group consistingof 2,2′-bipyridine, 3,3′-bipyridine, TMEDA, EDTA,1,2-bis(1-piperidinyl)ethane, and combinations thereof.
 20. The systemof claim 17, wherein the nitrogen-based ligand is a secondary amine,tertiary amine, or combinations thereof.
 21. The system of claim 20,wherein the secondary amine, tertiary amine, or combinations thereof aresubstituted with alkyl and/or aryl groups.
 22. The system of claim 12,wherein the ligand is a sulfur-based ligand.
 23. The system of claim 22,wherein the sulfur-based ligands are selected from the group consistingof S-heterocycles, alkyl and/or aryl thioethers, or combinationsthereof.
 24. The system of claim 12, wherein the ligand is anarsenic-based ligand.
 25. The system of claim 24 wherein thearsenic-based catalyst is selected from the group consisting ofAs-heterocycles, tertiary arsine with alkyl and/or aryl substituents,and combinations thereof.
 26. The system of claim 1, wherein theconductive oxide is tin-doped indium oxide (ITO).
 27. The system of 1,wherein the metal oxide and/or mixed metal oxide is a photocatalyticoxide.
 28. The system of claim 27, wherein the photocatalytic oxide isselected from the group consisting of titanium (IV) oxide, hematite(iron (III) oxide), tungsten (VI) oxide, and combinations thereof. 29.The system of claim 1, wherein the layer, coating, or particles arephysically and chemically stable.
 30. The system of claim 13, whereinthe phosphorus-based ligand is selected from the group consisting of1,1-bis(diphenylphosphino)methane, 1,1-bis(diphenylphosphino)propane,1,1-bis(diphenylphosphino)butane, and combinations thereof.
 31. Thesystem of claim 1, wherein the layer, coating, or particles are tightlybound to the substrate.
 32. The system of claim 1, wherein the particleshave an average diameter of between about 1 to 500 nm.
 33. A method ofoxidizing water, the method comprising contacting water with the systemof claim
 1. 34. A method of oxidizing an organic species, the methodcomprising contacting the bond to be oxidized with the system ofclaim
 1. 35. The method of claim 34, wherein a carbon-hydrogen bond isoxidized.
 36. A method for reducing metal ions to their correspondingmetallic neutral state, the method comprising oxidizing water with thesystem of claim 1 at an anode and reducing the metal ions to theircorresponding metallic neutral state at a cathode.
 37. A method forreducing organic species by electrolysis, the method comprisingoxidizing water with the system of claim 1 at an anode and reducing theorganic species at a cathode.
 38. A method for reducing oxygen to waterin an electrochemical fuel cell, oxygen detector or oxygen scavengingdevice, with the system of claim 1.